Actually it was very easy to allow titan to tank, even emerald carby and ifrit with a little bit of hate management. Sure you were lowering your dps slightly but that isn't an issue for soloing. Low levels smn really needs them for damage soaking. Carby and Ifrit required a lot of healing, sometimes they would die anyway and you'd have to account for that either by prepping for an insta summon or by putting enough distance between you and the mob to resummon. As it stands low level summoner just gets completely chewed up by some basic world mobs or fate mobs. They need that damage buffer. And if they haven't changed the summoner job quests then they're goign to be a nightmare. Especially the titan one, there's so much DPS from the mobs in that one they used to chew through ifrit, and you can't leave the npc to handle it because they die and it's fail.

I know what people are going to say, low level blm doesn't have any damage barrier. Well no, but they have sleep and you use that a lot low level solo. They can also put out a lot more damage as spike damage so can spike > sleep > repeat if necessary. Or even burn it down before the mob closes the distance (though with the changes to MP costs of fireIII this may have changed since they get at most 3 casts of that now). SMN damage is a lot more of a slow burner.

The problem is everyone talks about their experience at high levels or in parties and says "ah it's all fine" but you can't balance classes completely around that in a game with so much solo content like hunt logs, challenges and fates (yes they're group content but you aren't necessarily IN a group). I keep saying it but SE haven't taking into account GETTING to 60 with these changes and soem classes have really suffered at their lower levels.