Every job being good is for the most part true. Obviously not every job is equal but no job is so bad that they can't get content done, especially casual content, the differences between the top tier of a given category and the lower tier is generally within 5%, with a few outliers that generally get buffed/nerfed.
For leveling, healer will be slower when soloing for sure, but a lot of the leveling involves running dungeons(because of the story and also because it's just very good xp especially the daily roulette bonus which is basically a random dungeon and once a day you get a massive xp boost for it). And for these, as per usual in mmos, healers have very fast queues, while DPS have long queues, so healers actually level just fine and probably faster than DPS overall, with tanks being even faster(but not as much of a difference as between healer and DPS, only slightly faster).
You could also pick the one option that lets you play both sides, Arcanist, which counts as both Summoner(DPS) and Scholar(Healer), and while gearing both can be a bit harder, you can keep your summoner geared with secondary stuff to do solo quests with, and then put all the good gear on Scholar to do dungeons efficiently with(and carry the retards that can't play).
If you don't care that much about healer really go for whatever sounds good to you. Note however that Heavensward jobs(Dark Knight, Astrologian and Machinist) unlock like really late since they're locked behind HW access which takes a long time, while Samurai and Red Mage will unlock instantly at 50(so if you want to play these you can switch right away) and Dancer/Gunbreaker unlock instantly at 60.