I'm not sure I'm qualified to answer this question for anyone besides myself. For me personally, I think I shoot better period simply because I go out and shoot more as opposed to not shooting because I'm tired of shooting X firearm. Second, I think fundamentals are fundamentals and carry across different platforms; but, what I think you do lose are the small intricacies of the way one pistol handles/shoots, though what percentage that is I don't really know. I've heard it put that one can get into the 85%-90% range of ability across multiple platforms versus 100% for one, but I can't really tell you if that's true. I think it probably depends on the person and how much they actually shoot.
To me it's whatever will get you out there to shoot. Because it isn't just about drills, it's also about enjoyment otherwise you'll quit doing it. People are busy, if shooting isn't a necessity and you're not enjoying it, what's the motivation. Even for some that it's a job related skill won't go out and practice because they don't enjoy it enough. That's just my opinion. Whatever you decide, find some joy in it.