Does it make sense to pursue two master's degrees?
I'd say, having two masters degrees could definitely help you if you consider the 2nd one as a back-up plan (in terms of research fields/directions) if you cannot find a good PhD position in the field relevant for your 1st (main) one. It should, of course, depend on the availability, so ideally, there should be higher competition in the field of the &quot;main&quot; one, and not vice versa.
If you already know that you only want to continue in the field of your &quot;main&quot; one, and see the 2nd as an additional line on your cv, I doubt it is going to help you much, maybe unless your 2nd one is more math-heavy than the 1st one (which is not the case, as I assume from your question). In that regard, considering your 2nd masters direction a back-up plan could be quite smart.
Yet, if your 1st one is more fundamental and your 2nd is more applied, one way I can think of how your 2nd masters could help you obtain a PhD position in the field of the 1st one is: if during your 2nd masters, you learned a specific technique, or software etc, which is highly relevant for the PhD project you are aiming at. There is always a bit of luck involved though, unless you make a thorough analysis of the PhD positions market a few years ahead.