A few additions:
We see that phasers can be "dispersed" by naturally occurring radiation:
[quote="TNG Season 3, Ep# 49: "Ensigns of Command"]WORF: Human life form readings from the planet.
RIKER: So, the Sheliak weren't hallucinating.
PICARD: Numbers?
WORF: Impossible to get an accurate reading, Captain. The high radiation levels are disrupting our sensors.
DATA: Hyperonic radiation also interferes with ship's transporters; they are now inoperable.
WORF: So are the ship's phasers.
...
RIKER: How can humans survive down there?
BEVERLY: They must have found a way to adapt. Milan's work in radiation sensitivity suggests it's possible. Perhaps with extensive virotherapy ... Until they found the answer, their mortality rate must have been staggering.[/quote]Since humans were able to survive down there, the radiation couldn't bee too strong .
However, the important part is that the disrupted phasers were useless. Now, that disruption can't be very strong, it didn't distort light or even kill lifeforms! That is not consistent with a strong DET-weapon - you can't "disrupt" such a weapon, the energy has to go somewhere. A strong DET-effect would also be hard to "disrupt" - you would need a lot of energy, which is clearly not present here.
However, it IS consistent with chain-reaction weapon - the radiation could "disrupt" the chain reaction, therefore stopping it. If NDF was purely optional, the phasers would have continued to work with their DET-component, yet we don't see that.
[quote="TNG Season 3, Ep# 49: "Ensigns of Command"]DATA: Hyperonic radiation randomizes phaser beams. But I believe I can improvise a servocircuit which will compensate by continuously recollimating the output.
ARD'RIAN: You're using your own neural subprocessors to build a smarter phaser.
DATA: Essentially correct.[/quote]This just confirms what i just said - without that adaptation that re-enables the chain reaction, their phasers are useless. No DET-weapon could be disabled in such a way.
[quote="TNG Season 6, Ep# 144: "Starship Mine"]PICARD (pointing a phaser at Devor's head): Who are you? What are you doing on my ship?
DEVOR: The baryon sweep uses a high-frequency plasma field. That phaser won't work.
PICARD: You're probably right (pulling out a laser torch), but I'm willing to bet that this will.[/quote]Yet more evidence that phasers are disrupted by radiation, which just doesn't make sense for a DET-weapon (such as the laser torch).
Oh, and regarding Federation doors:
[quote="TNG Season 7, Ep# 171: "Genesis"]DATA: It is large, approximately 200 kilograms, and it is heavily armored with an exoskeleton of some sort. The lifesigns appear to be Klingon.
PICARD: Worf.
(Worf punches the door, and the metal buckles from the impact)[/quote]Granted, Word was mutated at that point, but we clearly saw that Chewie in SW (who should be of at least similar strength) couldn't bash in doors we saw destroyed by blasters. Yet we never see a phaser destroy the flimsy doors used by the Federation.
[quote="DS9 Season 1, Ep# 17: "The Forsaken"]INT. CORRIDOR (OPTICAL): Wisps of smoke escape from the closed door ahead... Sisko and Kira run up. Sisko touches the bulkhead door: it's hot.
SISKO: Phasers at maximum... They both draw their phasers, stand back... fire together... the door doesn't give. As security and medical personnel arrive, Sisko and Kira examine --
ANGLE -- THE DOOR: ... which shows a deep scar but another stronger metal lining is not affected...
KIRA: Toranium inlay... Cardassian design, I should have guessed... (to a deputy) We're going to need a bipolar torch to get through it...[/quote]Phasers are useless against their doors, they need a specialized cutting tool. The visuals of the episode show that they burn of a coating of perhaps one milimetre in thickness - this is inconsistent with a high-DET weapon, where the energy would have to go somewhere.
[quote="TNG Season 5, Ep# 115: "Power Play"]RIKER: A concussive charge would blow out the security field. Then we could go in with phasers on wide beam. Stun everybody. Sort it out later...[/quote]Evidently, they can't use their phasers to blow out force fields that can be blown out by a chemical reaction (tough you could argue that it was some sort of technobabble). We generally see that chemical explosions can compete with ST-firepower, which is just flat-out impossible with Trektard-supposed firepowers. We see this in "Insurrection" where volatile gas collected by the Enterprise was able to destroy the pursuing ships, even tough their weapons couldn't do it. A few other examples:
[quote="TNG Season 4, Ep# 91: "Night Terrors"]DATA: When Tyken was trapped in a Rift, his analysis determined that a massive energy release might overload and dislocate the anomaly. Fortunately, his cargo included anicium and yurium, which he used to detonate a massive explosion. He then escaped through the ruptured center of the Rift.
GEORDI: But we aren't carrying anything that could produce that kind of explosion. Even our photon torpedoes wouldn't be enough.[/quote]Two unknown chemicals in unknown are capable of producing an explosion more powerful than their photon torpedoes. Note that there is an upper limit to the volatility of any chemical explosion, it just can't be millions of times stronger than any known explosive.
[quote="TNG Season 4, Ep# 91: "Night Terrors"]DATA: Sir, Commander La Forge and I have come up with a potential solution to our predicament. Perhaps the modifications we used to increase firepower against the Borg might be effective here.
PICARD: Channeling power into the main deflector dish...
DATA: I believe within six hours we can generate a concentrated burst of energy which might disrupt the Tyken's Rift.
...
DATA: We are ready to discharge the main deflector, Captain.
...
GEORDI: Deflector power coils charging...
...
WORF: Discharge in three seconds... two... one...
...
RIKER: Nothing... it just fizzled out.[/quote]They need SIX HOURS in order to replicate the effects of a chemical explosion. Even if that explosion was made by a huge quantity of high explosives, that's still pretty damn unimpressive.
DATA: What we must discover is a means by which, working together with the aliens, we can produce an explosion more intense than either of us could achieve alone.
TROI: What is it you're looking for?
DATA: These are the elements we have available. Some of them could be used in the creation of an explosive reaction. If we can communicate this inventory to the other ship ...
...
TROI: "One... moon... circles... "
DATA: Yes, Counselor, one electron circles one proton... this is a hydrogen atom.
TROI: "One moon circles"... that's what they have been telling me... over and over ...
DATA: Perhaps the aliens are thinking as we are... to collaborate in producing an explosion. If hydrogen is combined with certain elements... calendenium, for example, it is extremely volatile.
They finally manage it - with another chemical explosion.
That just doesn't make sense if their weapons had gigatons of firepower, yet it is consistent with megatons of firepower.
Oh, and regarding the question "why are phasers that good against shields" - they could simply exploit the frequency-based shields in order to cause more damage (partially bypass the shields), which photon torpedoes could not do (since their explosion can not be carefully calibrated). That's also consistent with their highly variable effect against shields - sometimes they hit the right frequencies, sometimes they don't.