So in your example of how to deal with a wizard easily, the badguys ambush the PCs, get the drop on them, the wizard has no defensive buffs, they can easily walk right up to the wizard and ready their turns, and the wizard never moves away from the baddie. Seems a bit...specific? And it relies on a whole lot of things.
Also, how is the fighter flying?
Again, I've never seen this much effort go into "stopping" the rogue or the paladin or the ranger or the fighter. It's only with wizards.
Yes, but a person casts the spell.