At least on Light I haven't seen any obvious cheating.

There are few cases where 1v5 can happen but those are incredibly rare because it would need the 5 to be mostly clueless new players that stand together clumped up and not pushing their buttons properly. Such as GNB getting their full duration LB+AoE on team of squishys and maybe a hit or two to remaining players if they have enough hp to survive. DRG getting their buffed up AoEs into free LB. NIN getting a free full chain LB to already soft team. SAM getting LB to whole team tickling him during the counter. etc. etc.

Unranked to Gold isn't too bad if you have some experience and don't meet other higher ranked players, if you get to freecast as BLM for example you can just dish out more than double the player damage compared to next player on low level games.