Yeah, I've had little problem taking gyms by just doing repeated attacks - you just have to get the prestige down to zero, so 1 or 2 weaker people with enough revives can pretty much clean house. Holding the gyms is the hard part I think.
When I first heard that multiple players can fight in the same gym battle instance, I got excited with the hope that there might be the conventional raid versus boss combat mechanics present - a main tank, positioning being important, taunts and so on.
Of course gym battles are a lot more simple and fixing the many issues both combat-wise and in general take priority compared to adding such mechanics in.
It's also very difficult to design for mobile devices - not due to processor or screen size, but due to unavoidable latency spikes on LTE. You'd essentially need an in-universe explanation to reconcile conflict resolution with user expectation. "But my move registered and I stunned that guy, but he still killed me!"
