Again, I would start with questioning the validity of the underlying premise, i.e., considering extremely short duration records of activity is not a valid way to compare volcanic arcs. A more valid comparison would be things like total magmatic productivity (including both extrusive and intrusive) per unit arc length, total eruptive products per unit arc length, or similar. The question then becomes whether, when viewed in a valid way, whether the Andes are more magmatically productive than the Cascades. I don't know the answer to this (and it's not readily apparent from a quick glance at the literature), but that's really the first step, but as we'll see, an inherently challenging step.

With respect to the proposed hypothesis, i.e., that subduction rate directly ties to volcanic production rate, while logical this ends up being problematic, or at least not simple to demonstrate. It does have some support in the literature, i.e., there are studies that find relationships between estimates of volcanic activity and subduction rate (e.g., Huang & Lundstrom, 2007, Syracuse & Abers, 2006 - note for this last one, the Cascades are not even included in the compilation), but this correlation breaks down in other studies (e.g., Acocello & Funiciello, 2010). There are a variety of other things that have been argued to influence volcanic productivity, e.g., instead of the rate of subduction, the degree of obliquity of subduction (e.g., Sheldrake et al., 2020, Gazel et al., 2021), regional stress state of the overriding plate (e.g., Takada, 1994) - which is not wholly independent of the degree of obliquity or subduction rate, or the extent of hydration of the subducting slab (e.g., Till et al., 2019, Cooper et al., 2020) - which itself might correlate to things like slab age which in turn could correlate to subduction rate, amongst other controls. As highlighted in several of these papers (most prominently Acocello & Funiciello and Till et al) though, working out any of these controls is problematic because of a variety of challenges that mirror the issues mentioned in the first paragraph. For example Acocello & Funiciello suggest that the degree to which magmatic activity will or will not correlate with subduction rate depends on the time frames, i.e., plate rates are often estimated over long time frames than magmatic activity and whether you see a correlation or not depends on whether you take a long or short term view of magmatic activity. They also touch on the inherent issue with defining magmatic productivity. This is really picked up on in Till et al. where they discuss that (1) estimates of surface eruptive volumes are often highly uncertain and (2) estimates of intrusive volumes are even more uncertain. Importantly, apparent temporal or spatial changes in magmatic productivity based mostly on surface volumes may largely reflect changes in the intrusive vs extrusive ratio (which might depend on things like stress state in terms of whether magma is able to reach the surface or not, etc). So, essentially, we are still stuck with inherent challenges in truly assessing whether a particular arc is more productive than another. Suffice to say and as originally stated, one thing is for sure, specifically that an instantaneous snapshot of volcanic activity is definitely not the appropriate way to compare volcanic activity.