The key monk flaws are:
-Low AC - bypassed by specific builds, but generally lower than other characters without feat investment until the mid-late game.
Off-set by higher Touch AC and Evasion (serious factors when a single Empowered ray can drop a wounded fighter in his tracks -- and I've seen more character death by that exact method than any other in PFS play).
-Low damage - 3/4 BAB means Power Attack is weaker, while using Flurry limits your ability to apply strength to damage, all other 3/4 BAB classes possess their sources of supplementary damage.
<Glengarry Glen Ross> "Always Be Flurrying!" (That's what shurikens are for -- plinking distant targets after dropping the guy you're in melee with.)
As a multi-attacking specialist, they don't get bonuses which apply to each hit outside of damage dice increase, which at an average of +1 damage every 4 levels, is frankly embarrassing.
You mean,
automatic increases to damage? Well, aside from a barbarian's rage increase (which are just as slow), what other class gets automatic increases? Fighters have to spend feats, and then their bonuses only apply to the weapons they picked. When all properly pimped, that fighter will do better in an endless no-rest dungeon slug tailored to burn out every other class' uses-per-day. But the fighter still has garbage saves and worthless skills, so there's balance.
-- A monk isn't nerfed when he stops being
as good as, or better than, a fighter, at
fighting.
-High operating costs - Monk finds it more expensive to operate simply by having unarmed+unarmored being more expensive to bolster than armed+armored. Essentially they lose an item slot(weapon), on top of costlier equivalents
See previous post. That character could donate 100% of his income to "charity" (i.e., the wenches), and still kick ass harder than a rich fighter at 5th.
-High MAD ...
Due to the escalating cost of very high initial states, MAD isn't the killer argument I get the impression people make it out to be. I.e., a human with a bump in STR starts with an 18 for a +1 attack over my dwarf. But it costs the human 20 points to start with an 18 STR and a 16 CON, whereas the dwarf monk will be spending only 15 for 16s in both, leaving 5pts to throw as WIS...which will give him "free Iron Will" and extra attacks (via Ki). The fighter has better flatfoot AC and worse touch.
All those ki abilities run off your hotly contested standard action.
Most Ki powers are activated as Swift actions.
-Scattered capabilities - Monk abilities do not build towards a coherent role, much like spellcasters. Unlike spellcasters they do not have sheer quantity of abilities or power in each ability to make up for it. ...
It's odd that you'd compare monks to spellcasters, since monks (especially dwarf monks) are the CRB melee class you want to throw into a roomful of enemy wizards first.