What next for my attacker squad?

I assume you mean C/DP for Machamp.

Go and find some Ttar raids.

Evolve the L29 Gastly. TM to Shadow Ball (fast move doesn't really matter). Don't power up either Gengar.

You can already do Porygon with Machamp, Poliwrath, Dragonite, Raikou.

Scyther with Golem, Raikou, Flareons. Entei only if you powered it up, a L20 Entei is only going to drag you down.

Machamp, no. Alakazam needs Future Sight. Try farming Dratinis and getting a Dragonite with Hurricane.

Gengar might be possible if you can get Shadow Ball on the L29 Gengar.
Alakazam, Espeon, L29 Gengar, Dragonite. Focus Blast only. You probably need Ttars for Sludge Bomb or Shadow Ball. Rhydon might work for Sludge Bomb, but it MUST have MS/Eq.

You need to bring those pokemon to higher level breakpoints in decisive matchups
(Now Ho-Oh) (potentially Mew2)
For Ho-Oh: Raikou 35.5 (15def), Golem 39.5 (15att)

The better question is, why they need to solo anything? Wasting resources when you could be building a proper army for when PvsP comes.

i) porygon you can already solo: Machamp, poliwrath, raikou, Espeon, dragonite. Should be enough.
ii) scyther maybe: golem, raikou, flareon, dragonite.
iii) not yet, your fastest route is to tm alakazam to FS, get another Espeon (regardless of iv, find a high level eevee), and power up Ho oh with ES/BB. then you have alakazam, Espeon x2, exeggutor, Ho oh, dragonite. Should be good.
iv) power up the legacy gengar, he is much better than a non legacy wonder. Than you should be able to solo a FB gengar: gengar x2, Espeon, alakazam, dragonite, gyarados. Dodge FB with the first 4 and tank with the dragon and gyarados. If you still time out, get another Espeon instead of the gyarados.

"The current metagame is not kind to Fire-types, but they are crucial for soloing Scyther...." Umm, what? I think you mean Golem. To solo Scyther, get yourself 3 strong Golems. Power them up to level 31. Put them at the top of your Scyther lineup. After they are all knocked out, Scyther will be in the red and you'll be about halfway around the clock. Easy from there with almost anything reasonable.

To solo Machamp, I'd get another Espeon, and try to get a Ho-Oh with Extrasensory and Brave Bird (since you don't mention a Lugia with Extrasensory and either Future Sight or Sky Attack). Also a Dragonite with Hurricane would help, but that's not an easy get. I've also had good success with Scyther with double Flying moves - he doubly resists Fight, and Machamp is weak to his air moves. But don't use him against Heavy Slam, his advantage is almost all gone against Steel attacks.

Against Ho-Oh, since your Golem went down in one hit, I assume it had Solar Beam. Solar Beam is a totally different animal than the other two attacks. Brave Bird or Fire Blast can be fought successfully by 5 level 35 players with good counters, Solar Beam takes seven. Best success against Solar Beam is to use Dragonite, dodge the Solar Beams (not hard, you dodge a few moments AFTER the "Ho-Oh uses Solar Beam" message pops up) and hit it with as many Outrages as you can between the dodges and Dragon Tails. (There's probably a better way to dodge than that, but I don't know it.)

For Tyranitar, find a raid group, and take some down. Much faster than walking one (although that's good too, I still don't have Pupitar in my pokedex), and you get 10 Ttar candy if you make the catch afterwards (or 20 if you're Brave enough to use pinap berries).

If you can, build up a Eggy with Bullet Seed and Solar Beam. Good for Omastar, Golem, Rhydon (if he ever comes back), Kabutops (if he ever comes), Vaporeon and Gyarados (in Gyms), and probably some Gen3 that are weak or doubly weak to Grass. However, if there's a better Gen3 user of Solar Beam, do that instead, so wait on this until Gen3 is out there and understood.

Porygon is almost as easy as tier 2 raids, you should be able to do it easily.
Scyther you should be able to do with Golem, Raikou, Flareons. Dragonite DT/OR doesn't quite have the DPS for this matchup but can finish the raid in case you're worried about your team fainting and wasting time with rejoin.
Commented about Machamp and Gengar in another post but you should be able to do some movesets with the mons you have now.