Yeah, I doubt the "cleaving" method was ever intended, but I guess they never really did anything to stop it (maybe limit a bit?). At least they seem to acknowledge that it may affect other players in a negative way (the recent changes to the Crawlers' Nest [S]), unlike in the past ("Summoner burns" in the Korroloka Tunnel come to mind). I guess the location in this case being pretty new in a way, and there being limited areas for this activity probably had an effect in decision making.
I always avoided leveling up that way even during the Abyssea times.
Regarding master levels, at around 14, I think I'd get around 300-500 off of the colibri, making a level in about an hour or so alone with an alter ego party (one battle taking 30-60 seconds or a bit more I guess). Not horrible yet, but it seems it will become that very fast (indeed very much reminding me of trying to get to level 20 and above, solo, back in the day).
I suppose in due time they'll add rings and events that will make it more doable for everyone, but even with all the boosts for capacity points, it still took quite a bit to get 10,000 job points for a weapon upgrade (think I got around 100 per hour during bonus time, alone, and of course there's the weekly limit one could turn those in too, which is always a fun way to make things take longer (no, it's not, really)), so not much looking forward to actually grinding these in.
Guess they'll slowly come in due time... or not. ^^;