But I am not, because I don’t think I’ll be doing 50 km/h all the time on the flats.
More realistically, it’s between 30 and 45 km/h, so I will be spending most of my time in the 17- to 13-tooth cogs. Regarding spinning out, as soon as you go downhill, you can spin out anything. I haven’t ridden a standard crank in years, but I have had a loaner with a semicompact crank. The difference to my current bike with a compact crank wasn’t that significant. There were I think only two places where I’d spin faster than I’d like with my compact and felt more comfortable on the semicompact. On most downhill, once I hit 60 km/h I stop pedaling (unless I am racing perhaps). So in my experience, once mountains are involved, you can spin out any gearing if you are brave enough (or have just very, very little traffic).
On my new bike, which is being built up as we speak (they are waiting on the power meter AFAIK), I have chosen my gearing very deliberately based off of my experience with my current bike and the terrain I will be riding.
Overall, you should get away from chainring size and think about gear ratios. A 46-tooth chainring with a 10-tooth cog gives you a slightly taller gear than 50:11. Likewise, if you want the equivalent gearing of a semicompact crank, go for 48/35. In fact, 48:10 = 4.80 is essentially the same gearing as 53:11 = 4.82.
The new chainrings come from pros who not only spare their 10-tooth cogs, but also their 11-tooth cogs and many other smaller cogs. That’s simply down to marginal gains due to higher drive train efficiency, but has zero to do with them “needing” a 50:10 = 55:11. That’s why pros nowadays tend to prefer 11-32 and 10-33 cassettes despite the larger jumps and inhumanely large chainrings.