Thing is, though?
Fou-lu shows far more intelligence than the demons Yuri fused with. As we see in SH games, Demons *CAN* overpower the minds of those who they fuse with (Rasputin ultimately subjects to Asmodeus, for example), and Yuri was basically overwhelmed by Seraphic Radiance at that (there's a reason he went psycho for 6 months; it required Alice to go into his mind and basically help tame the thing. FURTHERMORE, the game basically said that his father (a far more experienced and likely more powerful Harmonixer) was suppressing the things power, though the game is never quite clear on this.)
Fou-lu strikes me as far stronger mentally than Yuri, for starters. Remember, the reason Ryu, someone who is ACTUALLY THE OTHER HALF OF FOU-LU couldn't absorb him was cause Fou-lu was greater; Fou-lu couldn't absorb Ryu cause Ryu resisted, and his friends gave him the strength to overcome that. Its only when one submits to the other (Bad Ending: Ryu agrees with Fou-lu that humans are pathetic. Good Ending: Fou-lu discovers the qualities of humans by fighting them and realizing that, despite they're flaws, they CAN do some remarkable things and have amazing potential, and ultimately gives himself up due to that)
Keep in mind also that when Yuri fused with Seraphic Radiance, it wasn't focused on him, AND all hell broke loose. Everything else Yuri had to fuse with, he had to FIGHT first. Basically, one instance where Yuri tried to force Fuse caused him to go all psycho in rage; all other instances, he still had to fight. That's kind of the point of the Graveyard and all that; Yuri fights a demon, beats it, fuses with it.
Amon is no exception to this either; yeah, he originally gained its soul through beating Albert Simon in Amon, but he still fought Amon in some form.
I'm not buying that Yuri's little Seraphic Radiance thing is something he can do on a regular basis; that instance was bizarre. In fact, Albert Simon even goes out of his way, IIRC, to inidcate Yuri's strategy is pretty whacked.
Regarding the Shanghai destruction thing?
Umm...A-tur destroys most of Chedo too, you know (all that's left of Chedo are tents located outside the city walls, which is just an excuse for one final weapon/armor upgrade really <_<). AND he was openly opposed by a good portion of an entire Empire's military there too, more or less. He still did it without even trying (think they say he wiped out most of the army single handedly at that.)
Now, why does A-tur matter? Cause he's Fou-lu's subordinate. The game is pretty clear that he's inferior to Fou-lu. If A-tur can do that much, this says a lot about Fou-lu's capabilities.
So...what's not to respect here relative to the Shanghai burning?
Edit:
No, Shale, you're wrong. In the case of Seraphic Radiance, he fuses with it...and then lacks the ability to control it. He needed an external force (ie his father's soul) to supress the damn thing just to live. He ultimately fights it to actually gain control of it.
He fights all other souls as well. Just trying to say "He gains the souls on the spot!" is silly.
If he did, why didn't he, I dunno, fuse with any of the Yamaraja's and just call it a day? Why didn't he fuse with Messiah from Simon and end the crisis there? Fuck, why didn't he just fuse with META GOD just to avert the crisis?
The answer is simple: He can't.
What about Rasputin w/ Asmodeus, Nicolai w/ Astaroth, etc? Its implied those demons were dormant, and that those two grabbed their powers while they were asleep (ALTERNATIVELY! They made a Demon Pact of sorts, that granted them their powers in exchange of something else. As CK once theorized, doing so can totally wreck someone's mind, as the demon slowly takes them over. It also explains why Albert Simon's personality is so different between SH1 and SH2. Believe SH2 even says he only fused with Amon as to stop Asmodeus, I think?)
I dunno...relying on one shakey example that had CLEAR DOWNSIDES to prove your point doesn't really strike me as much. From what we see in game, Yuri actually has to fight to Fuse.
What about Kurando? That seemed more awakening his inner potential than anything else, at least for Jutendoji. Tsukuyomi seemed to force its way into him, not the other way around.
Based on what we see, I feel its a stretch to say Yuri can walk up to any sort of being that isn't clearly mortal, fuse with them, call it a day, with no obvious repercussions. ESPECIALLY one that shows a lot more sentience than what we see in SH games.