You absolutely need strong units if you want to mess with the other stuff.
You only need to worry about specifics if you care about T20 Arena. You can get into the T18.5 bounce with Askrs. Note that the T18-19 bounce gives a very minor less resource than 20 (1300 Feathers difference, that's 1 5* Promo every 3, almost 4 months) . By all senses it's a waste of an opportunity cost to play T20. Between TT, T18.5 Arena, and VGs, you'll get all the feathers you can ever really need. Especially if you play wide instead of tall, much like a City should be.
It throws ~250 free orbs a month at you and hands you all the tools you need to do Infernals and Lunatics.