They are actually not, almost every class can access two attacks at lvl 1 all they have to do is offhand a proficient weapon most of which are a bigger damage die. Rogues for instance has a similar starting ac way more options for scaling ac early and does two attacks very easily at 1d6 now the monk gets to add stat bonus for free at lvl 1 however the rogue can easily take dual wielder to close this gap. Additionally every time the rogue sets up a sneak attack situation which only requires a suprise assault or one ally also threatening. they automatically get the same damage as an additional hit so theoretically an optimized lvl 1 thief has more attacks and more consistent damage than a lvl 3 monk. the monk has far less access to magical items in raw, they have to this point been in about 0 of the modules released by wizards of the monk hate. The dodge action as a bonus action only applies if you are spending KI which means you wont be flurrying which means all your damage calculations are incredibly inaccurate. multiclassing slows access to the very important lvl 5 power bump to 1d6 and the extra attack which they need to stay steady with fighter and barbarian WHILE SPENDING KI. while those two other classes with hulking HP pools access to damage reduction and magic on every slot of thier character do the same damage without spending resources.
I had a lvl 5 arcane archer fighter with burst shot do 102 ranged damage in a single round and everything he used besides a scroll came back on a short rest. only 1 crit, because flame arrows.
Tons of spell effects specifically target a weapon which you cannot do for a monk in raw, you can magic weapon the staff but the extra attacks are all non weapon attacks and don't gain the bonuses, while a warpriest that has the same amount of flurries with martial weapons at lvl 1 that a lvl 3 monk has can gain the benefit on all hits.
