It’s a little hard to make an absolute determination, but it’s quite likely that someone at your level will see your raw strength drop while doing mainsite WODs.
CrossFit is about being really good at the middle ground and until you started it, you’ve been way at one end of the whole strength/fitness spectrum.
If you carry on as you are, given time you’ll find yourself weaker than you were, but not as weak as you would be if you stopped training, so still pretty strong, but much better at everything outside of powerlifting. Which is what you’re seeing.
At this stage I’d be reluctant to suggest any additional strength work as the key to adapting to CrossFit is recovery and if you’re as heavy as you are, you probably need all your recovery ability to let your body adapt to what you’re making it do now.
Hard to give a time when you could safely add in more strength work.
Possibly, when you’re completing Pack level scaled WODs near the target time? Or maybe it’s when you’re feeling recovered between workouts.
When you’re sure that adding in extra work isn’t going to hurt you, add in some powerlifting training each week. A bench day, squat day, deadlift day. That’s the simplest version and there are many, many more.
You’ll probably need to get into custom WODs at some point and that will let you bias your training to the strength end.
I doubt that you’ll retain as much strength as if you remained a full timer powerlifter, but you should be able to stay in touch with where you were.
Mainsite WODs are necessarily about general fitness. They’ll get you strong if you’re weak, but if you’re a dedicated strength athlete, they will diminish that as you balance everything out.