Pass. This seems overly easy. Instead, I'd prefer that retainers didn't entirely lose proggress in previous classes if you changed their current one (i.e maxed out MRD retainer, you want to change because you decided with the new expansion you won't level MRD first - so you change retainer's class to GLD and it starts out as lvl1, BUT you retain its old proggress in case you ever want to change it back to MRD for whatever reason).

Some items obtainable by ventures are quite rare, adding a way to cheese your way to these items seems... like a bad idea.

It's one thing to have these potions for your character as you NEED to level up in order to access most content, retainers however don't quite work this way, and can perform their core duties (which is to store crap) even if they remain at lvl1 forever.

Leveling them is easy as hell, you go to them and order them to go out for a couple of hours with items and a truckload of exp, and bam in little enough time you have a leveled retainer, your only loss being ventures