I can empathize with the suggestion, I disagree on principle because grinding new TDRC crown should be a thing people do to swap builds to play the game instead of skipping grinds.
For example right now most mage share gear except crown and weapon, if this is implemented then switching from SA to performer you just need to buy +12 A time dim that is really easy to get (below 300m, shout out to sophie services), which makes the game boring and economy stalling when the only transaction that is happening is just weapons.
Same with crit characters mostly sharing the same thing, easier access to endgame is a good thing but too easy and people get bored, noone will play/participate in the market which leads to a decline in the server.
Grinding TDRC is the game being re-playable, if everything can be shared between builds, then you just need to grind once and never play the game again, which is the opposite of the game being re-playable. That's my 2cents