If this was the case, especially for proposal three, every mage would choose either fly or their respective bash-protection spell.

An ABS'd, fully spelled up mage who is rolling is already a complete, utter pain in the ass to lag/kill. Making it so it's either very hard or next to impossible to dispel him would make these powerhouses even more powerful.

I really don't think there is anything wrong with dispel magic. Sure, in a gank it is powerful...but so is summon, or lag options, or any other number of skills/spells. Dispel magic on it's own just isn't that scary, and if your foe is focusing on that instead of something else...that's time spent not (actively) killing you (provided there's not an extenuating circumstance, such as dispelling water breathing underwater or a gank).

For instance, as a shaman...even though dispel is SUPER nice, 1v1 vs a mage I'm almost *always* communing something else.