Gear-swapping should not be frowned upon in PVP. It's been a key game mechanic in FFXI since its inception. A penalty (as I already mentioned, a 3 second bind effect should be more than enough) need to be in place to prevent people from abusing it while running away. That said, S-E could easily promote static sets of armor by instating caps on stats, attack, accuracy, m.acc, m.atk, evasion, etc while inside ballista.