ACCESS_METHODS_DATASET_PARENT Problem
Given the wait types of LATCH_EX and ACCESS_METHODS_DATASET_PARENT I highly doubt AlwaysOn was the culprit.

These two latch types may go hand in hand. You'll want to investigate where the latch_ex waits are actually happening - sys.dm_os_latch_stats may help here where the latch_class is not 'buffer'.

Given that removing AlwaysOn did not help with the situation, I highly doubt AlwaysOn was the problem. However, AlwaysOn may have contributed to some wait time though how much is impossible to say, though I doubt it would be noticeable against your current top waits.

Paul has some information on these:
https://www.sqlskills.com/help/latches/access_methods_dataset_parent/
https://www.sqlskills.com/help/waits/latch_ex/

Additionally this whitepaper on latch contention may be helpful:
http://download.microsoft.com/download/B/9/E/B9EDF2CD-1DBF-4954-B81E-82522880A2DC/SQLServerLatchContention.pdf