Having a movement skill does make certain encounters easier depending on the build but its not always neccessary.
Boss fights are a special instance as there are ways to get around this “get out of Dodge” issue simply by positional play and learning the fights. Even fights like The Emperor of Corpses (dragon boss) can be done with a decent pair of boots and no movement skill - its a little tedious to be sure, but not impossible with a little preemptive posititioning.
This issue is critical for Dungeon bosses - no matter your build - because the devs have designed the fights with attacks that cannot usually be tanked and WILL one shot you. There are some guides to these that imho, can make the Dungeon boss fights trivial with a little practise.
As for jumping damage, I havent really experienced this particular issue - I dont recall a jumping attack I cannot move away from. but yes, killing mid jump is an issue right now.
Usually the telegraphed attacks in normal mob fights are easy to move away from without movement skills - e.g. embermages nukes or lightning elementals blasts. Perhaps the particular jumping mob is highlighting a deficiency in your build / defences rather than being too powerful?