A Different Way to Play

[Chihaya]

SE sort of made class inefficient and jobs are much more efficient.

You are losing a great deal of damage going as arcanist rather than summoner.
You are dropping 20 INT just for the job crystal as well as some VIT/PIE for the HP/MP.
You also don't have access to your highest single target damage ability Fester - as well as pet damage enhancing Spur and special move Enkindle.
Summoner Egis are generally stronger than Carbuncles with better abilities (though they look like shit)

Tanking pets (topaz/titan) are generally considered a nuisance to tanks unless your tank is just terribly bad.

You can still cast resurrect as a summoner, and there is no point for a dps to be casting protect or the crappy sub-level50 10% hp stoneskin when a physicks is going to heal more than that.

You may choose the way you want to play, but don't expect everyone to accept it and not frown upon your decision.

Only class I consider ok is Marauder, since when you do this, you are more interested in putting out damage as a tank role rather than actually tanking. Not saying they can't tank, but a WAR typically would do better (minus the perfect dodge).