Can it use magical defensive devices e.g. a Ring of Protection or similar?
Otherwise, I'd say the issue isn't that it starts with AC 14 - AC 14 at 1st level is fine, all things considered - it's that said AC doesn't increase fast enough to keep up with level-appropriate challenges.
I can't offhand think of a better way, though, that keeps Monks viable at low levels yet doesn't give them ridiculously good AC at high. Maybe knock off one of the Wis or Dex bonus but allow them to wear light armour?
Or give them some sort of dodging ability so they don't get hit quite as often? This could be something flat, that doesn't increase with level, making it more useful at low level than at high (by which point they've got other things going for them).
Yeah the issue is't the starting AC. Hide and Ring starts you at 14 AC. It's that armor users get to 17-18 AC very quickly. Armor users can use shields. And bot armor and shields can get AC bonuses.
A monk with 14s can only start with 14 AC and if they bump DEX or WIS can get to 15 AC. Whereas every warrior, priest, rogue, and bard is 16+ AC minimum. This is with the monk having the HD of a rogue AND worse weapons AND worse skills.
How this got past playtesting, IDK.