well once you unlock elites, u will be already 80 😄 core elementalist is much worse for solo exp than mesmer. Im mesmer main. But if i should choose what is better overall for comeback player and what is more complex in the future expansions. Then i would say ele.Its harder, so u will get the mechanics u can later use on the other classes. Because once u unlock the elites. Ele has much more varriety while mesmer is basicly the same (keep using same weapons, even the ambush mechanic only adds a small piece to his gameplay in pve on mirage spec) until you hit the cantha and unlock virtuoso spec. Ideal class for comeback and experience expansions is ranger or guardian. Both are easy to exp 1-80 and then both have very special varriety of elite specs that you really want to try out.
Just my opinion.