Playing RTS style works until chapter 3 when AI goes crazy bananas with Warlocks. You cannot ignore dragon-mode and win. Sadly.
It already went crazy for me with them halfway through Chapter 2.
Warlocks are very effective for AI as they are a micro-heavy unit, something the AI is naturally good at.
They are cheap and massing their Rain of Death can knock out half your army if you aren't careful.
In principle it's easy to counter them e.g. in Dragon mode, but I still found it a pita.
They maybe should be nerfed a bit by reducing their range, the effectiveness/durability of the cloak, or adding a build-up for the damned Rain of Death.
What I'd also like to see are some actual missions outside of "destroy the enemy" in the RTS part. Larian could maybe couple them to General sub-plots or random story events.
As for cards, it was brought up a few times during the beta, but I don't remember any comments from Larian on it:
I think some possibility to trade cards would be great. Right now esp. for the dragon cards I almost never feel the need to use them, since I either have researched the skills, or don't use them anyway. Same goes for the "build unit x during one round" cards. Both are ok to good early on, but quickly become outdated.
Adding a building that lets you trade in unused cards for some new ones would be cool.
Something like "Pay three cards, choose a new one from the same type" or "Pay two, receive one random card (probably same type as well)".