I believe this case is very badly handled in this data structure implementation. It seems to be saying that you want to occasionally manually recreate the DS as it grows bigger, as the deqs won't automatically resize. So you'll just have linear behavior in that case, with extra constants because the deqs are useless logic.

I suspect an amortized data structure could automatically and internally do this rebalancing operation, but I'd have to work out the scheme and the analysis. At a guess, something like normal dynamic arrays do, where you multiply the max size by a constant when it fills up, would give you decent amortized bounds.