Double tap is going to have been removed primarily for PVE reasons. Maybe PVP was further supporting evidence but ya’ll need to remember WoW is a PVE game first and foremost and a PVP game after the fact.
If they thought double tap was fine in PVE 0 chance they’d remove it.
Going out on a limb and taking a guess that double tap was making MM impossible to balance in PVE as it is in PVP, and so they’re removing the major culprit so they can adjust MM away from the “nuke the world every 1 minute and afk otherwise” thing they’ve had going on awhile now.
It’s likely to be a healthy and overall good change for MM in the long run for both PVP and PVE.