jaymatt19-we must have different prints of the seder hadoros.Mine-first part- only goes to page 296.Anyway- the first part has many names (as a mafteach-index) and it includes the name “chaim’ many times.Of course- that name has been around since middle ages-and the tosfos that you mention is in the middle ages. In the second chelek,where he brings down the names of the tannaim and amoraim, chaim does not appear.
BTW- “hiyah” in aramiac means life-just like chaim. maybe this is what you refer to. Nonetheless- the question of many posters remains: why can we -and we did- make up names throughout the centuries and just now we cannot?
derech hamelech- plenty of ‘chareidi” gedolim saw no problem with the name shira (see posters) so this is R”chaim kanyevsky vs. other chareidim.