Monk wasn't a "high end melee contender", it rendered obsolete basically every melee build save maybe bards:
PM? Why bother. Be even less killable with monk, better AC, edodge, permanently capped ms and SR.
Classic fighter based WM? Why bother? The monk variant, while a chore to level and gear, was functionally better than both the 2h wm and the 1h wm.
Rogue? Looked really good on paper until monk 2.0 was mentioned, and then it was just kind of a worse way to do all the same things; they both livelord, they're both oppresive af to fight. The rogue is just mortal, and occasionally dies when he makes bad mistakes.
Ranger? Niched already to archery, -guardbait dps STRangers, and dex based livelords. The two melee variants soundly eclipsed, because monk filled both the livelord dex build and the str -guardbait role way better, and with fewer weaknesses.
Barbarian? Not really meta right now because so much has eclipsed them as far as unkillable melee contenders (rogue, druid, etc.), but monk just added insult to injury there.
Now monk has been reduced to the role of "highly survivable and mobile harrasser". They have a good slew of immunities, enough SR to keep themselves safe from UMD and a lot of NPC casters, which is a big deal. They've got stealth, good AC, the ability to extend into edodge, reasonable if not stellar damage; it's like a rogue that trades DPS for survivability.