To be clearer, I should have written 'a calculation' and 'a computation', as in the examples of the older usage, 'compute' is a singular noun, referring to a specific calculation, and the acceptability of substituting, under current usage, 'compute' for 'computation' here (where the latter is shorthand for computational work or effort, rather than referring to a specific calculation), has no bearing on the usage five centuries ago - and nor does the usage five centuries ago have any particular relevance for today, given how much computation has changed since then.

I think compute stands in for computing power so `amount of compute' to me means `amount of computing power'. If I were to use the terms calculation or computation I'd pluralise them so you'd get `amount of calculations' and `amount of computations' from `amount of compute'.