Oh yeah, you spend all your Ki points on flurry and then you get walloped on the crackback and you end up at half HP in one hit because you have 15 AC and only D8 hit points despite being stuck in melee all the time! You know a Rogue could out perform you with like a hand crossbow and sneak attacks and stay out of enemy reach with minor action disengage without spending a single ressource. And they get expertise on top.
This theorycraft isn't born out in actual play. Most 1st-tier monks I've seen blast through an average monster by spending a single ki point on flurry when they decide to nova. d8 hp doesn't mean you get one-shotted, so you can take a round or two of hits (and a round or two is all you need), and 1 ki point left in reserve lets you access the defensive options if the monsters get lucky and crit you or something. Dead monsters give no crackback. Heck, the most recent monk I've had was effectively the party tank (a cleric, a warlock, and a bard made up the rest of the party). The comparison to a rogue is pretty apples and oranges - remove ki and you may as well remove sneak attacks, too. Expertise is a ribbon.
And Stunning Strike is a friggin' trap. Your saving throw is often way too low and it's just another thing to burn your Ki on that only seem to work on enemies you were better off just attacking so your allies could finish them off before they act again anyway.
Again, not borne out in play. Big secret that most wizards know is that monsters have doo doo saves. Sure, dragons or giants or other meaty critters might save, but you've got enough ki to take it to them round after round - everyone rolls a 3 eventually (typical D&D fight is about 3-5 rounds, so it's not like you need to conserve your resources much there). I've seen monks lock down enemies often enough that house ruling Stunning Strike is one of the few power-based house rules I've considered for 5e, due to it turning so many 4v1 fights into cakewalks for the players (didn't end up doing it, because I prefer to allow power to breathe a bit, but it wrecked some fights like
arcane eye wrecks some dungeons!)
Nah, compare a Battlemaster without Superiority Dice to a Monk without Ki. The Monk sucks at everything.
That's still pretty apples and oranges. Different classes have different subclass budgets. Fighters get a lot of very solid features from their core class (which is a problem for putting Warlord in Fighter, since there's not a lot of power budget to work with!). Also, Fighters are arguably one of the most powerful classes when it comes to damage.
The game's group PvE, so you want to compare the monk to the rogue or fighter in terms of matchups against monsters of various CR's with various party members, rather than comparing raw damage outputs. Do they contribute enough? My XP says yeah, though their ribbon-to-attack ratio is a little borked (enough so that spending ki on other things, like an elemental monk's spells, has been seen as a downgrade in play).