I got here also 3/4 bets a second, even with low bets. Probably the bet amount doesn't make any sense about the roll speed.
As you said, the speed does not depend on the bet amount. The number you roll is determined by some mathematical calculations and the bet amount does not matter.
The speed depends on "rolling speed" you set in autobet setting. But that depends on your internet connection too.
It also gets affected by the VPN as well, in the end if you have too much stuff in between the casino website and your click then there will be some delay. VPN affects it, ISP affects it, internet speed affects it, basically everything that affects your internet also affects the website as well.
Like for example, a person who downloads a movie in 10 minutes and a guy that downloads it in 2 hours will not be able to roll at the same speed, there will be difference at the same time. That is why I honestly feel like game changes time to time because my internet connection is not stable, if I use ethernet its always the same exact speed but I am usually in living room when I gamble which is why I connect with wifi and my wife watches netflix at the same time so my speed always varies.