But the introduction of that LFG tool (more specifically the raid finder) also coincides with the start of wow bleeding subscribers, and they haven't recovered since and instead just kept bleeding.
I don't think there is any evidence that there would be less players in wow if they never introduced that feature, on the contrary there are plenty of things pointing in the opposite direction.
But other games that have a Raid Finder are doing well and rapidly increasing their player numbers: Final Fantasy 14 has had the exact same system since the beginning, and it's definitely not hurting their growth. I think that, despite the hate it gets, LFR was far from WoW's main cause of downfall.
The phrasing made it pretty clear that their issue was with the LFG tool and that you get ported to dungeons when using it to level.