Nice debate!
OK, if I'm going after anything bigger than a racoon, I'd use a PB because I don't have a Texan in .45. However, I wouldn't use a .22LR for much above a racoon. Even a fox, I'd want a quick, clean kill with good 150 yard plus range. That means more in the lines of a .223 or so. Others are more confident in their hunting skills with a 22LR, but for me, 22LR is more of a plinking round, maybe up to racoons and that's about it. It can do more in skilled hands, but for me, nope!
So, changing the narrative from airguns shooting slugs compared to .22LR, to next move being a .223, the slug fills a niche for me. It's plenty to take rabbits at longer ranges, racoons and such, and if you live in a municipality where discharging a PB gets you a police visit and handcuffs, slugs are definitely a better way to go.
The other thing I don't like about PB's is registration. The silencers are registered, the guns are registered, the laws around the guns are much more restrictive. Why trip into that area of life? In this case, the slugs are more practical from a legal hassle standpoint. Just don't want to deal with the Feds on any level.
As for cost, I already own airguns. While the Impact isn't the best to shoot slugs, it will do it, but I'd probably use the Marauder to shoot slugs right now. It's already here and heavily moderated. My shooting would not be more than 50 or 75 yards. for me to do the same with a .22LR, $400 for the gun, $200 for the tax stamp, not sure how much the silencer costs, probably into the setup for at least $1000 or more. Decent .22LR is running $.08 per shot last I looked, and slugs around $.15 per shot. So, if the difference is $.07 per shot, I can shoot 14,285 slugs before slugs actually cost more than a new .22LR setup.
This is a classic debate in so many ways. I have this conversation whenever I go to the range with my son's. One shoots a 45-70, the other a .50 Beowulf. We punch holes in paper at the range. After one or two, twenty round boxes of ammo, at $30 per box, they are ready to go home, more because their shoulders are in pain. I'm just getting rolling at 100 rounds, and just getting in the groove. I can shoot all day on $18 worth ammunition. Can I convince them to switch to airguns? No way!
Then for cleaning, of course, I just put my guns away, they have another hour of work to do outside in the snow.
Whatever you decide to do, it's right for you! The argument for the practicalities of a PB over slugs are endless, but I'll still be shooting slugs just for grins and giggles.