that might be it, i remember GTA-V had problems on xbox360 i you got the digital version, the single hard drive couldnt keep up. so it had lower draw distances and specs patched in. but if yo had the disc, it would install the whole disc, and then run off the disc and the hard drive at the same time.
i recon defiance suffers from the same problem. in fact now i think about it, a clan mate on xbox had the digital version only, and always complained about lagging out, then he got a disc copy for the loot the ultimate gives, havent heard him complain as much since.
so try a disc copy... if you are in the UK/EU i actually have a PS3 copy doing nothing....
Needs to be said, the ps3 you bought is the last gen version. The one with the cheapest crappiest components. Sony did the same thing with ps1 & ps2. Ps3 slim is the top dog for reliability, had mine 4yrs and its never broke down.
As for critting out, I wont take trions side because I dont think it should happen as much as it does but there are a few things to consider
1. This is an mmo
2. Its on a severely dated console with crappy ram
That said the game was built for multi platform & like you said has been out two years. Anyways, reloading often is key. Once an hour, or after going in and out of instances a few times. Its a good habit to get into, at least you'll be deciding when to reload most of the time.