I’m fairly amused at the TP challenge turning into a 3-hero team of 5*. Generally speaking, it is implied that the TP quoted on an offense is for a full 5 hero team because you are simulating the gameplay for someone whose roster maxes out at that TP. Consolidating the power into fewer higher defense/attack heroes likely makes things a bit easier.
That doesn’t mean it is impossible. It made me think of this gem back in the day:
I forgot about Muggy-Mania during Season II. 
Those days only S2 was out and I think emblems were around, but were still a more recent addition. I’d be interested to see if 5 Muggies with few emblems could take out today’s diamond defenses. These days, it might worthwhile to have Gramps on the team to revive them all again for another round!