Rayquaza as Machamp counter

Rayquaza isn't as bulky as Dragonite but has better DPS against Machamp. I'd say it's better as an overall Machamp counter but if you need more tankiness, you'll still go for Dragonites.

EDIT: Checked quickly on pokebattler, Rayquaza has 2% less power but a whopping 20s faster time to win.

I personally wouldn't power up a Dragonite for Machamp at all. Alakazam, Espeon, Gengar, and Mewtwo will get you ahead of the clock. Ho-Oh, Lugia, Kyogre/Entei/Moltres (For Steel sets) and Gardevoir (For Fighting sets) will keep your survivability up.

Rayquaza will only further demonstrate that Machamp doesn't require the level of prep that some people are giving it.

Dont need another Machamp counter, it already can be defeated with no duplicate (unique challenge) without legendaries, even without dragonites also
And the squad doesnt need to be max out either...