senda and qot aren't really good late game. They're also not good against a team of disables.
examples of teams that can rip them apart:
any combination of reg, UG, oak
TB + any of the above will also work if TB is built correctly.
Against a DPS'er, qot's late game shield goes down in a couple seconds. Plus, if you have mark of the betrayer on her, just casting it makes it start with less than half health (800 damage out of 1.4k). Late game, they don't tend to deal much damage. If they go for health items, they end up dealing practically no damage.
I think the demigod heroes seem pretty well balanced with the exception of dupes. Dupe regulus seems a little overpowered when built properly, but that may be because I haven't figured out how to beat it yet. Dual DPS reg isn't bad. Dual assassinate isn't bad. Dual mines is crazy. They can out 12 mines between the two of them. That's 450*12 = 5400 damage aoe they can lay out in 10 seconds! The only thing that can clear it is cannon fodder that generals can summon. Maybe erebus can do it....