Sharing some results for soloing Machamp
I have always been a fan of the raid guides on here, but sometimes for new or casual players, without proper counters, you may wonder if you have what it takes to solo some of the T3 raids. After hitting my last break point with my Lugia, I wanted to try out my Machamp team. It was simple and finished with 40 seconds to spare. But that made me wonder if my son's account could solo Machamp. He has some legendaries, but not much fire power being only at level 28. I tried 2 different teams, here were the results.
Sunny Weather-Machamp with C/DP
The first team was my best stab at it with what he has. Account level 28.
Espeon cp 2258 zh/fs
Mewtwo cp 2458 pc/sb
Mewtwo cp 2517 pc/fb
Dragonite cp 2875 dt/o
Latios cp 2485 db/dc
HoOh cp 2829 sw/fb
As you can see, none of the movesets on Espeon or Mewtwo are ideal. The result was not great. The Mewtwo were just at too low of a level, and without confusion and psychic, they didn't pack enough of a punch and there wasn't enough time or fire power to rejoin.
For the second team, I simply went with the suggestions.
Espeon cp 2258 zh/fs
HoOh cp 2829 sw/fb
Gyarados cp 2785 s/hp
Latios cp 2485 db/dc
Dragonite cp 2875 dt/o
Exeggutor cp 2475 sb/SoB
As you can see, the auto select removed the Mewtwo and added Gyarados and Exeggutor. You will notice the Eggy is double grass, but with sunny weather, grass gets a boost, so it was probably my next highest DPS pokemon (not weak to fighting.) This was actually a very close fight. The Machamp KO'd my Eggy with 8 seconds left and the Machamp had just a little bit of life left.
Conclusion-If this auto selected team had very slight improvements, it would have gotten the job done. Probably something as simple as having a level 30 Espeon with confusion, having a better moveset on HoOh, having Extrasensory as opposed to bullet seed, or simply making 1 more dodge. I hope these results encourage lower level players, or those without the best counters, to give the T3 raids a shot. Thanks for reading!

Answers
Level 30 non-legendaries can get the job done. Exeggutor and Espeon are easy to acquire, so no reason to not have at least one with optimal moves. Depending on biome, Alakazam and Dragonite may not be that hard to obtain. Gardevoir and especially Metagross are rarer (the later still eludes me) but are not required for easier Machamp sets (especially if you dodge well).
I agree. I have seen some people around here still worried about T3 raids tho, which is why I posted this. My son's account is very casual tho, so actually the legendaries are more accessible. He isn't even close to an Alakazam, but Espeon was a simple name trick. I guess the take away is that you don't need the counters listed in the guide. You can use pokemon like Gyarados in the team to get the job done.
This is what i use for soloing machamp (level 36 here)
Cp 2559 lugia extrasensory/sky attack
Cp 2713 espeon zen headbutt/psybeam
Cp 2806 ho-oh extrasensory/fire blast
Cp 2504 gardevoir confusion/psychic
Cp 2416 latios zen headbutt/psychic
Cp 2020 lugia extrasensory/hydro pump ( just use this for extra bulk because lugia double reists fighting)
PS i dont have mewtwo yet but i have my first ex raid next thursday so hyped for that
The problem is, they want to do it or not.
I play alone on weekdays, so other than i like to do it, i have to do it if i dont wanna stuck with T1-2 raids
Many people including high level trainer in my weekend area still duo or even trio T3 raids, because they used to and dont (want to ) know how to prepare for it.
Ussual excusse is short on revives, they wanna do it quick, etc
FTM the Espeon to Confusion/Future Sight. FTM the Ho-Oh to Extrasensory, and preferably CTM it to Brave Bird (it's weak, but it's fast, and does SE damage). Even Solar Beam is better than Fire Blast - even with STAB, FB doesn't cut it.
I've never been a fan of FB Mewtwo, but some people like it. TMing that to Conf/Psychic or Conf/SB would make it much more effective, especially with Psychic.
Do you have a double flying move Rayquaza on that account. It's surprisingly effective against Machamp, even at level 25. Latios and Dragonite will hold you back, even with the higher CP on D'nite.
And work on Alakazam with FS - very effective. Even Dazzling Gleam can do good work in a Machamp raid, even though you don't get STAB with it. A couple of glass cannons backed by Ho-Oh or Lugia is the usual recipe, and I assume the account doesn't have a Lugia since you didn't mention it.
Just keep working it - you'll get there.