I don´t understand why SE doesn´t implement an account based bank with sufficient slots.

The technology is already ingame with FC banks. They could get rid of the retainer inventory which seems to cause so many problems. And the game would be much more alt-friendly.

I try to level all DoL/DoH and spend already a lot of time managing my retainer inventory and the MB (with 8 retainers). Sure, I could further optimize the available space, but switching between retainers, searching for mats that are momentarily not needed and worth posting on the MB is just not fun for myself.
I would prefer to spend this time with crafting, gathering or playing my DoW classes.

Having to spend 10 extra euro per month to avoid the most of tedious work in a game just isn´t a good design.