Still, as human beings, we try to find patterns where there are none. I do believe that the new slots pay better than the old ones (conspiracy theory ), and guess what, till now this has worked. Whenever a new slot releases, I try to do 200-300 spins at the lowest bets and usually hit a couple of bonuses with decent payouts. 
IMO, it pays less after being emptied by streamers screaming from the bottom of their lungs with fake money . My hypothesis is that the new slots pay out to the lower stakes, which attracts a lot of fish nibbling, which ultimately attracts whales.