Why? You need a basic with 3 energy on it and 1-2 stage 1s on the bench which have pitiful health as both a basic and a stage 1, just to OHKO an EX and then not be able to do it again for 3 turns? No thanks, I'd rather go with Blastoise and BKEX which can OHKO an EX every turn with only one benchsitter.
No, it isn't. Switch/Keldeo EX are prevalent now and so stopping them from retreating is rather meh. That's also a lot of setup and very inconsistent just to 2HKO EXes when everyone OHKOs you back for 2 prizes or just kills Altaria extremely easily.