I've been a spinner for years. I used to mash, years back when I did time trials and commuted in London. I was certainly faster as a masher, but I suspect that has more to do with the passage of time than the technique.
For the past three days I've been doing a short hilly ride each morning, keeping the gear on 42x19. That's been fine, of course, and seems to allow me not to spin out until about 32 kph on the downhills. At 28 kph it's a comfortable cadence, and TBH, the majority of my cycling is about 22-28 kph (except on hills). So ... I thought 42x18 seemed a reasonable size to go for. I'm not sure I agree with the proposition that it won't do anything for strength, as it's much higher than I've been using on some of the percentages.
OTOH, I can now accept that at some point I'll have to give fixed a try. I can see that it must be a fine feeling to be remain involved during the descents.