You have to realize that the expansion you're seeing is a result of striking a hard surface. Bone ! High power center fire projectiles will do that just passing through the ribcage and then into high liquid content internal organs. It's all about hydraulics. Most airguns just don't obtain enough velocity to achieve those kind of hydraulic results.
I've found a good expanding projectile can make a huge difference with "hydraulics."
Polymags, for example, open a cavity and leave a large wound/impact channel that you don't see with diablo's.
I've seen a hollowpoint turn tissue to mush and create an exit wound much larger than the entrance wound.
In my experience, it provides extra insurance which can make the difference between a runaway and dinner.