Assuming Tom is correct, I'd bet a dollar the other developer he's referencing is Mediatonic. Fall Guys looks to be in a mess with slow updates, level vaulting (that was accidentally reversed for a few hours), and loads of technical issues. Also, just based on public charts, Fall Guys has lost a bunch of players. Outside of losing most of its Steam userbase, it is in the mid 20s on the Xbox charts and down to 18th on the EGS charts. It had been in the top 3 for both charts during its F2P launch. While there is a natural playerbase decline for F2P games, Rocket League is still chugging along and has actually grown quite a bit the past few months going from about 500k peak CCU to 900k (but still far away from its F2P launch peak of 1.8 million in 2020).
I don't think there's any immediate danger of Fall Guy getting Rumbleversed, especially since Epic owns those devs and isn't simply acting as publisher, but it isn't doing nearly as well as before and Epic has shown they will willingly kill underperforming games.