Mobility creep isn't really a problem when a lot of immobile champions are strong
All competitively viable with higher then average winrates and reasonable popularity in SoloQ.
Most of these don't even have dashes or speed boosts.
There's tonnes of immobile champs who are used competitively but do just fine in SoloQ roo.
is pretty sleeper OP too. His mana costs are ridiculously forgiving.

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on that list