But it's not a 1v1 game (well ptr excluded), the biggest part of Zarya is the ability to shield an ally who is being frozen to break the freeze from happening. Almost any of the dps classes will beat mei if they get a zarya shield to prevent the freeze.

The same goes for lucio, i play A LOT of lucio but if i get a mei on me then all i can do is boop and run then hope its enough. However if one of my team mates starts to get frozen then simply a boop away from my team mate is usually enough to prevent the freeze and force the mei away. The same goes for lucio vs the ult if you hear the mei ult then switch to speed and speed boost when you see the circle almost always your team will escape the ult.

There are a number of situations in overwatch where a 1v1 favours a character but the tools of many characters change that in a team fight. The biggest example is Roadhog vs zarya, in a 1v1 it usually favours the hog but if you focus on shielding every ally hooked by the hog you essentially nullify the impact a hog can have on a game often forcing them to switch.