I'm a bit late to this discussion but this is my take on it after taking Machamp through Ranked mode for a ways:
Machamp is prefectly viable on his own, but may be hard to stick with as a solo main. Machamp has some matchups where you're going to have to work hard and which feel unfair but which are generally very easy once you get in even just one time such as Braixen or Gardevoir. Your success will depend quite a lot on your ability to block consistently and to make properly timed use of your counter attack options. You need to be prepared to deal with frustration and some matches feeling unfair or like you couldn't do anything if the skill disparity is too great. A lot of times you're going to be forced into a guessing game on wakeup, but you do that twice as hard to anybody you knock down in duel phase.
As a character Machamp is more support dependent than the rest of the cast but this isn't a bad thing, Machamp brings out the strength and utility of a lot of supports moreso than any other character as well. Whimsicott, Diglett, and Rotom/Magneton are noteworthy in their ability to cover weaknesses of Machamp depending on the matchup; Whimsicott should be a 100% take in the Shadow Mewtwo, Gardevoir, Chandelure, and Braixen matchups unless you are VERY confident without it. Even Ninetales can have some nice utility in the Blaziken, Charizard, and Weavile matchups where Machamp actually has advantage in terms of projectiles in field phase.
Overall Machamp is a strong character who is downright terrifying to face on wakeup or when backed to a corner, which can happen very quickly thanks to cross chop and forward X or frame traps such as Jab 2->Submission or Body Slam->Up Y->Close Combat pushing the opponent a long ways across the screen. The character also has a distinct advantage of having none of their projectiles cause phase shift, so you're free to throw rocks and focus blasts for tons of damage in matchups where your opponent is forced to approach you, a nice bonus that I don't see many Machamps take advantage of. Also, empty jumps into Air Grab are awesome, seriously, people forget you have that tool all the time and will just block or begin charging a counter. It's worth an enormous amount of damage.
That was a lot of text but that's about how I feel on it now. tl;dr Machamp is a hard character to play solo who is heavily support reliant but really really rewarding to succeed with.