Listen here, I don't know on which private server you were playing but it wasn't far easier on retail. And definitely wasn't even close to current heroic.
Exact top 200 guilds and duration it took them to kill from first to last boss:
T13 (10M HC)
1st boss: Dec 7, 2011 18:20
Last boss: Feb 10, 2012 19:27
Total: 65 days
T13 (25M HC)
1st boss: Dec 7, 2011 20:54
Last boss: Feb 22, 2012 20:57
Total: 77 days
T15 (10M HC)
1st boss: Mar 13, 2013 20:31
Last boss: Jun 20, 2013 18:37
Total: 99 days
T15 (25M HC)
1st boss: Mar 27, 2013 01:56
Last boss: Aug 6, 2013 02:35
Total: 132 days
T16 (10M HC)
1st boss: Sep 18, 2013 20:37
Last boss: Jan 28, 2014 19:28
Total: 132 days
T15 (25M HC)
1st boss: Sep 18, 2013 02:39
Last boss: Feb 7, 2014 05:30
Total: 142 days
Nyalotha 20 Mythic
1st boss: Jan 30, 2020 18:12
Last boss: Apr 5, 2020
Total:
66 days
Nyalotha random amount of people heroic PUG
Total ~5 days (at worst), prolly cleared day 1