The Present
Weapons (and presumably Spirit) have worse cooldown mechanics
Right now, when Magic and Fighting use a skill as an Ultimate Art, other skills of the same type that are NOT ultimate arts are placed on a normal cooldown.
Example: I use an Ultimate Art Javelin on my main magic. My normal Javelin on my 2nd magic is placed on its normal 75% cooldown, and then I can proceed to use it normally. The same applies for FS: I can use Ult Crash on main FS, then normal Crash on 2nd FS.
This does NOT happen with weapons (I assume Spirit as well, since they use the same skill slot system. I have not personally tested it).
If you use an Ultimate Art Tempest on one of your weapons, for example, ALL Tempest skills will be unusable for the duration of its cooldown. This prevents you from using skills as both frequent “normal” skills and ult skills. While you can still alternate ults to compensate for this, it just feels worse than with Magic/FS.
The Fix
Apply the same CD share system for Magic/FS to Weapons/Spirit. To compensate for the increased slots the latter have, the base CD share could be 75%-100% compared to Magic/FS 50-75%.