>>30901128>lucario and blaziken>too strongnon-speed boost blaziken was outclassed in every way by infernape and even back in gen 4 lucario was never "good"
while there's some clear bias like charizard and mewtwo getting 2 megas each and some blatantly unnecessary megas like salamence, a lot of them went to either unpopular pokemon (kangaskhan, pinsir, houndoom, medicham, etc) or popular but not very powerful pokemon (heracross, ampharos, absol, mawile, etc)
Other than the aforementioned favoritism for a select few like charizard and mewtwo which I previously mentioned the biggest issue is the disparity in how well many of them got changed in the mega evolutions. Some clearly had special treatment in how their mega was handled (Lucario, Charizard, somehow Beedrill managed to get super minmaxed, must be a dev favorite) and some are poor to outright bad (Audino, Houndoom, Glalie, Latios all spring to mind)
the mechanic is good but was handled poorly, like a lot of things in pokemon these days actually