Or they could simply go back and "fix" Arcanist, so Summoner (and to a lesser extent, Scholar) gets fixed through it as well.
And once again, it's already way too late to separate them from a story/lore standpoint, which has been solid/consistent since ARR.
Also, you keep forgetting all the supplemental resources that rely on Summoner having Egis around (trailers, artwork, CG renders, encyclopaedia, etc.).