The percentage level of decline in Bitcoin has always been different in the time period you mentioned and yes it is also the rate of increase in every four years because Bitcoin is not at the same ATH in every four years. That's the evidence that many people have seen by now and the possibility for a major upgrade cycle over the course of every four years, I think will still be there and happening in Bitcoin.
But as the cycle continues the percentage will not be the same obviously. The rate of increase might be somewhat lessen as compare to the previous run. It's because the price is really very high or going to a level that not everyone can invest a lot and only the whales will have the money to invest huge amount. In any case though, we average joe can be part of the next bull run, just invest small and what we can afford in this bear market. And maybe in the next bull run, the price will be in the 6 digit
Percentage may of course change, which it has every time we have gone up, but the idea that it will be bigger than the last ATH will stay, we do not drop too much further anymore, we do not stay at ATH anymore, that's what the cycle means.
Last cycle we went from under 1k to over 20k and dropped to 3k and never seen under 1k again, this cycle we managed to go over 20k ,and seen it reach 68k and drop to around 18k at lowest and never seen under 10k again. Next time around I guarantee it will be over 68k, and it is going to be something like "never see under 40k again" or maybe 50k who knows. That's how it progresses, so it gives ease of mind to me for sure.