Leveling alts now is a waste of time if your goal with leveling an alt is purely to fill out some kind of completionist checklist for your alt stable.
If you enjoy the leveling process, then it’s not a waste of time.
If you hate the leveling process, but have an alt / class you want to try for endgame anyway, then it’s not a waste of time.
The expansion is too far out to hold back on things with the intention of waiting for it. Unless you’re planning on outright unsubbing for the next 9-12 months.