About kill steal, i think it's fair game, otherwise that precious seconds can get any friendly assets destroyed by the opposing asset (not just CAS 'stea'l other's kill but in between tank sq members that are engaging same target as well for example)
Another example is when both CAS heli & APC engange the same Shilka, with APC dumping a few rounds already, it's only logical for CAS to kill it A.S.A.P, because otherwise the Shilka will be more than likely to switch it's attention towards said CAS and proceeds to kill it in a matter of miliseconds..
It's a different thing if the 'kill stealer' intentionally going for other's kill when he himself should have taken care of something else instead.
For example CAS in Muttrah large should prioritize taking out mortars most of the time if the mortars are active instead of trying to kill armor/inf and raking up kills because CAS is the only asset that can reasonably take out the mortars efficiently with the least amount of risk
About apt. spawn on basrah, it's totally broken, you can get 60+ in less than 5 min. you can basically keep shooting every half a second and bots won't even have a cance to aim at you, let alone escape.
a good CAS crews could even cover both apt. & palace at the same time without any real trouble.
In the end, if everything was still under control & everyone was doing their intended roles without breaking any rules, it goes down to opportunity, experience, communication, and sometimes luck