I wouldn't object to dilithium being critical for all conventional warp, regardless of the power source. That is, you always have to pump that power through a dilithium crystal if you want it to become warp power: it doesn't matter whether the power comes from m/am annihilation, fusion, a spare Kelvan outboard engine, the burning of coal or the frantic pedaling of 4.7*10^18 hamsters, it needs the dilithium as a filter anyway.
We know that there is magic involved in warp drive at some point: it's fundamentally unreal. We can decide where to draw the line, but drawing it at lumps vertenium cortenide going FTL when energized with real-world power isn't the best way to go. Warp plasma itself is already magical to a degree, as in "Fair Trade"; not just any old plasma will do there. And dilithium is a magic material by its very nature, while m/am annihilation is a known thing in reality, so drawing the line right there should work fine.
We have never had a pressing reason to think Romulans could manage without dilithium (which they mine from Remus, say), and now we have a pretty pressing storytelling reason to think that they couldn't. This should tip the scales on the otherwise ambiguous AQS power issue nicely enough.
Timo Saloniemi