But it'd be so, so, much more useful to just have it on something you'd wear anyway.
It's definitely more useful, but not at all interesting. I find this very similar to the suggestion of allowing multiple sets of nyame armor. It would be really handy to have nyame for TP, WS, nuking, debuffing, etc. Especially with the DT and Meva. But it creates a lot fewer decisions.
It's like when your best DD piece is also the highest DT and Meva...well there's no reason to ever use anything else.
If the best pet DT pieces were also the best master DD pieces on PUP or BST, it would be useful and convenient, but also boring. Same with wyvern DT, or wyvern absorb in this case. If it's a good TP piece and also good for wyvern absorption, you aren't actively choosing to equip it to keep your pet alive, which makes the game less interesting and engaging IMO
This whole discussion spawned because of that and this idea is novel and niche. In a world where empy head had STP+12 and DT-12%, this discussion would never happen because it would be the default head piece.