Soloing stuff gets you way more PP than not. But, that's only if you don't value your time at all (unless you can auto-battle the fight reliably). As long as you end up at 150+150 with 4m PP it doesn't matter.You got to 150 Reds? Then you're fucked, sorry. Also, sub 4m PP and 3 star means that you got one from gacha already.
Thankfully, this is the last raid event where you can get fucked over like this. So uh, that's good, I guess? Doesn't help you much though...