If u wanna shoot slug. Get a gun that is made for slug. Just throwing slugs in a gun and hope it shoot accurate is like putting all your saving into the PowerBall lottery and expect to hit that jackpot.
Your analogy is funny, but not sure all guns are made equal when it comes to slugs.
As just one example - I have a RW .22 HP Safari that shoots the JSB RDs at 970 FPS pretty accurately at distance ( 100 yard paper targets ). When I use the JSB Knock Out slugs which are also 25G, it does shoot better at various distances. At 50 yards, it shoots much better than the MRDs in my barrel. At 100 yards, it also shoots better at times, but the MRDs are pretty fair as well.
To your point, in my RAW HM1000x .22 HP, slugs do not shoot well in that Poly barrel.
The MRDs do shoot well. So, I think some guns can shoot pretty well with either pellets or slugs. I am also aware that the FX slug liner fans have a bias towards using those slug liners too; again to your point of using only a slug gun or liner/barrel to shoot slugs.
Lastly, some shooters want to get the most out of their guns and would prefer to have guns that can shoot both pellets and/or slugs. Others, like to separate and use their guns for just slugs and not pellets. This is one of those discussion topics that have an " it depends" set of scenarios. Just my opinion, not fact.
Tom