Squires get one of the best all-around useful skillsets in the game, most notably accumulate and gained JP Up. Move +1 is also really handy early. Accumulate is a great all around skill to have. Both for powering yourself in battle and for self-sufficient spamming for JP with a broken enemy.
Basic skill is at the very least useful through the game, and it'll be a while before you really have dedicated things to trump it in any capacity.
Many classes are basically just gateway classes to better ones to begin with. Ninjas, Summoners, or Lancers are usually your best bet late. Ninjas with Move+3 are rather broken though.
Also, you'll need very high level squire to get most of the big classes anyway.
Its a game whose difficulty curve will, for the most part, scale down pretty badly for most of the game. Most late game fights aren't really a threat.
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Never underestimate the power of stupidity in numbers. ~War13104
Never stoop to the level of idiots. They will drag you down and beat you with experience.