sechel re Mashiach being from the dead: we see in gemara (at least according to the simple meaning and many rishonim) it was done
How many times do we have to go through this? The “simple meaning” is that they were telling us the name of Mashiach, whoever it will be or was. Not that they claimed their Rebbes were Mashiach. Note, the gemoro asks מה שמו – what is his name – not מאן הוא משיח – who is Mashiach. As I wrote, they may possibly have meant that their Rebbes were Mashiach (probably while they were alive), but that is NOT the simple pshat.
Furthermore, I have searched and have not been able to find ANY Rishon other than Rashi on this piece of gemoro. So please name the “many rishonim” you are referring to.