This is the same thing as brawl, as you indeed mentioned in your post. I went into significant detail about this a few years ago and Peach was an example I used and fits perfectly with your description here
http://smashboards.com/threads/marg...el-vs-perfect-play-and-bad-characters.302972/
My argument is that if a character is so mechanically demanding to the point that no human can reliably play the character at maximum efficiency, then they can't be rated on potential. There is literally no reason why I cant say that a mechanically perfect Samus is top tier, just no one is capable of using her to that level yet apparently Ryu is a special case.
Ryus inputs arent hard, his combos are pure muscle memory (you can do them with your eyes closed). Yes he does take more effort to play than Mario for example, thats obvious. But at no time does that make him a good character. That essay I wrote is long but it talks about that in depth, high difficulty with high reward in a character does not make them good. Reliability is what matters, reliability to win matches and matchups that matter.
Personally, I believe Ryu is very overrated because he cant force you to do anything. When he gets in, its disgusting what he can do and focus attack is absurdly good. However, you can predict and react to his linear approaches, his mixups on approach are bad, projectile is weak and hes slow.
The best characters in this game force the enemy to play on their terms. They dictate the pace of the match and there's nothing you can do about it. No character can force Rosalina to be aggressive, what can the majority of the cast do to stop limit break charging and playing in a permanent state of fear vs MK makes people do dumb decisions. Ryu is too slow and lacks proper defensive tools to dictate how any top tiers dismantle his gameplan.
I am not remotely suprised, and 100% expected that those two players would stop using Ryu. They are both very smart, very technical players that excelled with complex characters because of how far they could push them. Ryu has a big fat hard limit on how far he can be pushed and its because he quite simply doesnt have many options in neutral. Defensive Ryu relies on bair and hadoken which are trounced by anyone with a projectile and attacking Ryu just doesnt have the speed or range to reliably get in and start his devastating punishes.
Those two players would have been very frustrated in how they feel they should be doing better, they know they can push the character far and they have the intelligence to do it but they got caught out when other characters run circles around them or put up such a strong defensive wall that you cant get in. Its like, if someone found a way for Ryu to reliably get in then he would be unstoppable but for 5 or so months its been the same old story of Ryu players getting walled out so hard that him being able to KO early is the only thing keeping him viable in the first place.
I think Ryu is good of course, but I think he is below
and shares similar viability to
With poor representation in japan and europe and NA's #1 Ryu player apparently on hiatus as his other prominent secondaries have mostly returned to their normal mains resulting in his results tanking hard, there is no way Ryu desers a spot in the top 12 of the cast.