The TM MP7 has always been crap and something to stay away from
G&G's are only entry level, usually not very good, but highly upgradeable
Your King Arms' problem isn't the gun itself, but rather the person working on it.
With the right parts and service, there's no reason your KA shouldn't be able to last 2-3 years without breaking down.
If I can build a high ROF, high FPS, high performance, 11.1v LiPo, SW-COMP equipped LMG, that goes 3 years without breaking down internally, then a lesser skilled gundoc should have no problem making a low performance gun last 2 years. Especially with the vast amount of part knowledge available on this site.
The biggest factor in maintaining and fixing AEG's has always been the gundoc's mechanical aptitude.