The argument that glass cannon characters have their offensive capabilities being "balanced out" by their relative frailty and therefore should be less eligible for nerfs hasn't held much weight in any fighter in the history of ever. They're (almost always) still extremely dangerous characters in spite of that. Capcom never balances Akuma by just lowering his health every update and calling it a day.
Smash still follows character archetypes of fighting games despite not having the same core fundamentals. You have your glass cannon characters, you have big burly bruisers that are hard to kill, you have your defensive zoning characters, etc. The same way Bowser can take a lot of punishment before losing a stock is the same way Zangief can take a lot before losing the round. Smash is not a unique snowflake in that department.
Those last two sentences are where, I believe, you are misunderstanding the concept of health CORRELATED with losing the game and health CAUSING you to lose the game. Also, stocks and rounds are not the same.
Bowser can take a lot of punishment before losing a stock, however, Bowser can also take very little punishment before losing a stock.
To put it into perspective, bowser can take two punches at the beginning of a stock--> grabbed--> thrown off--> then gimped on his last stock which leads him to losing the game. Zangief can take 2 jabs at the beginning and NOT LOSE THE ROUND for all the rounds he is given. As I mentioned before, the probability of you losing a round after losing all your health in a SF game is 100%. In melee, you can lose a stock no matter what the percentage is and you can also keep a stock no matter what the percentages is. Because of this, we can not compare the two games because even though, as you stated, CHARACTERS may have similar fundamentals between melee and SF (which I also disagree with but we wont get into that), the fundamentals of WINNING AND LOSING are not the same.
If a character has lower health/easier than kill than almost anyone in the cast (on paper), but have among the best offensive capabilities of anyone in the game, guess what? They're still one of the best characters in the game.
One thing I want to point out is that it is fine if fox is one of the best in the game. BROKENESS is what we are concerned with not whether a character is extremely good. We all know fox is beast, but is if he is "broken" is a different argument.
Whether it's Fox, Akuma, Zero, Phoenix, Magneto, Taokaka, Millia, Akiha, whatever. Fraility DOES NOT completely balance out a character's extreme offensive capabilities. It never has, never will. So I'm not trying to hear because Fox can die and be comboed so easily (again, on paper. Never mind he's one of the fastest characters in the game and you have to catch him first), it justifies having a ridiculously strong and very safe up-smash.
Frailty does balance out the extreme offensive capabilities. That is why most characters you mentioned (I don't know all of them) are simply considered extremely good BUT NOT BROKEN. BROKEN was Sentinel (Im not sure if he is different now from day 1 sentinel in MVC3 vanilla) because he had INSANE offensive and INSANE defensive capabilities. Falco does not fall under that category. falco has AMAZING offense but **** recovery RELATIVE TO the MAJORITY of the cast in ProjectM (very important that I am not referring melee here). Unfortunately , people now a days group fox and falco so much because of melee that they actually believe that because fox has good recovery, then so does falco. That is not true at all, ESPECIALLY in pm where there are NEW gimping and/or off stage scenarios that falco CAN NOT come back from but fox STILL can. So in PM ,Falco has **** recovery. In melee, it was decent/ good at best because these new characters and scenarios were not available. So nerfing Falco's offense will hurt him much more than a lot of people think.
I believe people need to get the idea of "melee falco= PM falco because of frame data" out of their heads.
Now nerfing FoX 's upsmash specifically, on the other hand; I can reason with.
He has better offense than falco and OBJECTIVELY much better recovery than falco, putting fox at a category where he has INSANE offense and VERY GOOD recovery RELATIVE TO the MAJORITY of the cast.