It took me a while to warm up to Dyna Cabs. I get it.
Finding the right IR, or mix of IRs, can take loads of time to arrive at (at least for me it can). When you do finally get there, that tends to set a pretty high bar. At first I couldn't get Dyna Cabs to sound even close to what my preferred IRs were giving me.
I spent some time A/B-ing cab block channels between my IR selections and Dyna Cabs. After digging a little deeper and experimenting with the Cab & Preamp pages inside the (Dyna) cab channel, I was eventually able to get fairly close to replicating what the commercial IR combo was doing. Except with what I can only describe as better clarity. Which is the one thing I find most striking about DC in general: They're just so crystal clear and articulate. I've never had any commercial IRs sound like they can sound.
Dyna Cabs remind me of what my Two Notes Torpedo Cab wishes it could have been. Concept wise, their proprietary IRs were very similar to Dyna Cabs, but Dyna Cabs deliver so much more clarity, control and sonic detail (and it was part of a free firmware update no less). Price some of the Two Notes products if you haven't for some additional perspective. The addition of Dyna Cabs is an incredible step forward. I'm curious to see if they'll add more cab choices, or mic types. I have no idea, but none of this means you shouldn't use your preferred IR(s) if that's how you want to roll. There are plenty FM9 features I have yet to even touch, and I really don't feel obliged to use them until I need to.