Requiring a full-sized party for tank mount achievements is a bad idea. The notes say a full party will be required, which likely means Undersized Party must be disabled, and therefore you must sync at 50.

This is a bad idea because:
  1. Those achievements never encouraged many people to start playing tank jobs in serious content anyway. They just rewarded players who already did.
  2. It hurts people farming ponies and doing WT. It's hard enough to get and keep pony farming groups together already.
  3. No one does synced EX primals, and there's no reason to try to make people do it synced. The rewards are outdated and are just for fun.
  4. The time investment to get these mounts is long enough as it is, especially for people going for all 3.
  5. And finally...there's no incentive for ANYONE to do synced EX primals besides tanks. SE has just killed primal tank farming for level 50 duties and hurt people making groups for EX primals for ponies and WT.