Here are the BFA Season 2 ratings cutoffs for the Sinister Hero and Gladiator ranks.
As always, these ratings are not final, and they will change between now and the end of Season 2. This is a snapshot of what would have been if the season ended at: 6:15 p.m. CEST 24 June
Hero of the Horde: Sinister
Rating: 2521
Hero of the Alliance: Sinister
Rating: 2425
Horde Sinister Gladiator: Battle for Azeroth Season 2
Rating: 2868
Alliance Sinister Gladiator: Battle for Azeroth Season 2
Rating: 2970
Based on this (and the US post) and looking at the ladder this very morning (and checking which rank had the exact rating mentioned in the cutoff post):
Playerbase EU (top 114 Horde cutoff, top 72 Alliance cutoff):
114K Horde
72K Alliance
186K Total
Playerbase US (top 80 Horde cutoff, top 44 Alliance cutoff):
80K Horde
44K Alliance
124K Total
For EU, which had 412K valid participants in BfA S1, this implies a ~55% drop in participation, i.e. there’s less than half the amount of participants in BfA S2 as compared to BfA S1.
Additionally, BfA S2 has the second lowest ever participation of the seasons which we have data for. Although it is likely that many of the Legion seasons had lower participation (among Legion S2-S6).
You might be right, the original numbers here were apparently a few days old (since Arenamate had already had been given the original cutoffs by Blizzard informally even a week before they were posted here).