Yes, web fonts often suck on slow connections. Meanwhile, on fast-ish connections, I find the FOUC effect to be greatly annoying. That 1-2 seconds of seeing Times and Helvetica and then seeing Freight Text Pro and Proxima Nova drives me bonkers. I think there must be some kind of happy medium between FOUC for faster connections and rage-inducing FOIC for slow connections. Unfortunately, most devs (and sadly I claim to be one) don't test their sites frequently on a range of connection speeds so it's common to have badly-tuned font dynamics on sites.

Bottom line: as someone who cares about design and visual experiences, I don't think the answer is just accept and live with FOUC everywhere. Browsers and dev tooling both need to improve in order to find that happy medium.