I think on the whole, during the 'Golden Age' of slotting where Netent and Microgaming reigned supreme, most games were medium-variance, coupled with RTPs we all got rather accustomed to, in the what, high 96s? 97?
So naturally this resulted in frequent 'profits', a small deposit here and there, make £100 and Bob's your uncle.
Coupled with smatterings of reload bonuses to the point where you couldn't beat them away with a big stick, small or even medium-rollers could end up having fun, prolonged play time and a reasonable cashout expectancy.
All that's happened now is that the marketability and visual appeal of 'big wins' has taken over the medium, so that designers have focussed on high-variance games. That's erm, it. Everyone wants the Hollywood Hits but of course they come at a premium, and you can kiss your play time and bankroll goodbye too.
Throw in a healthy dollop of RTP-shaving and slotting on modern games has become an expensive sounds & lights show, less gambling.
I think the end user's experience and value for money is set to diminish further, but at some point it will become unsustainable, and we might see a market crash of sorts, and possible return to higher RTPs.
With the downside being that the UKGC will only permit players to have an overseeing 'Slot Custodian' monitoring your spin ratio, heart rate, social status, political leaning and of course 'feelings'