There are still MP issues, though not as many as there were at launch. A lot of people have left because of the game’s technical flaws, leaving the player population stunted. 343 has not had much to say recently regarding the remaining bugs in TMCC, but for the most part it is in a working state.
Hit me up if you see I’m on, I like to hop between H5 and TMCC. Love every halo but 4.
I don’t have issues finding games most of the time, but MCC multiplayer itself leaves a lot to be desired. Just don’t expect MCC to have the same amount of “polish” Halo 5 MP likely has, as dedicated servers don’t exist in this game.