I don't think you understand what toxic means , toxic means unhealthy because of parts are too hard to balance.
Kindred's old passive made the champion toxic due to how much power it had, tryn's passive is toxic since it's luck, zoe's w is toxic because it's rng.
None of those champions are toxic because of mobility and there mobility is not why they are good with the exception of irelia and MAYBE akali.
Zoe is good because she can easily take out one person, pyke is good because of his follow up, yuumi is good because she can easily poke people out, irelia is good because of her 1v1 power and bs weave clear.
Like mobility is not a problem it's utility that is the problem with most new champions.