Honestly, those solutions all seem a bit complex. I feel like the best option is to just keep it simple, with something like a single releveling is all that is needed to unlock all three Prestige options for that commander.
That would cut down the grind down to a third, essentially. Basically just need to Prestige once to unlock the alternate kits. Thus, this still require people to play through from 1-15 again to refresh themselves on each commander, but only once instead of three times. That way, one still has to work to earn Prestige options, but no longer is it unnecessarily long and grueling.
And of course, for those very few who enjoy that, the Prestige option is always there again for those to reset themselves to their hearts’ content. That way, everyone gets what they want. A way to start fresh now and then for those who like that kind of thing, and those who don’t like that leveling process don’t have to do it three times on each commander just to experience all their toys.
It’s a simple solution, and one that’s hard to argue against unless one is the kind of person who wants to keep stuff out of the hands of casuals for arbitrary or entitlement purposes.