zbattle on one hand is just the zsnes netcode that hasnt been updated in many years as well
zbattle really has no infrastructure to add to the netcode other than the “quarter system” which they set up, a unified place to find players who want to play the game
Kaillera built the whole infrastructure around its netplay, and used the server inbetween clients for error checking or some other dumb reason to balance it out.
Lag is more of a problem for kaillera due to its reliance on servers, which typically suck. Its better to just host your own private servers for 2 players to see a good performance, since the servers nowadays get bogged down. Not to mention the fact that the ping it reports is only refreshed once during connection, and is based on you to the server, and not on you to the person you are playing, which some people confuse for being some sort of accurate guage for lag. Also MAME has a higher system requirement, and if one side is slow, the other side gets bogged down for no apparent reason other than the faster side has to wait for the slow side to catch up… and god do I hate that shit.
and yeah, zbattle doesnt send as much shit, too bad I notice it dropping keyframes like crazy, I can live with the lag in kaillera exchange for no desynching and actually having moves come out.