Twinkruns are extra loot rolls for a select few in a twinkrun and then you pick the best players with the best gear for the real raidgrp, and that is like 25man gear in 10man raids during wrath.
So yes it is normal that a raidgp gets stronger each reset, but the "world first" contenders use the game mechanics that allow this kind of behaviour with gear funneling. And Paragon brought this behaviour to 10man raidgrps, where this gear funneling is much less common. (Granted, overall the amount of guilds doing multiple twinkruns for gear funneling is pretty small)
Champions with equal footing is not possible with rng loot and different raid setups even in the same raidsize, but abusing game mechanics to doule or triple the amount of gear received each week does not surmount to the the better raidgrp in my opinion, and it gets to the point where the ilvl advantage is to big an advantage.