Panther and Frida absolutely deserve ascension. They’re not just for titans! Plus Panther’s quite squishy.
The +attack trio (Miki, Tarlak, Ranvir) and Ares are okay at 3/70 until you start in on 14* titans. They should be a high priority for ascension, though, as they can also be very useful on offense (well, I can’t speak too much about Miki in that context, but I often use Ares or Tarlak on offense. (I never bring non-maxed heroes on offense.)
As I’ve observed elsewhere, most people think about offense as all about firing special damage at the foes. A tile-forward approach is also effective (if you know how to set up boards), and heroes like Miki, Tarlak, Ranvir and Ares are all about helping this tile-forward approach. Put them together with some mana-managers (e.g. Onatel, LotL, Hel) and ypu’ll get great results.