We're seeing this today with 10nm parts from Intel that have lower clockspeeds versus 14nm++ and even AMD engineers say they were surprised they could get clock improvements on the Ryzen 7 3000 family at all. The author notes that at least in terms of raw frequencies, the best seems to be behind us. Newer nodes aren't showing a promising trajectory for clockspeeds so the industry will have to rely even more on different methods to push the performance of chips to new levels:
This might seem a bit churlish to write in 2019. After all, we’ve seen more movement in the CPU market in the past 2.5 years, since AMD launched Ryzen, than in the previous six. Both AMD and Intel have made major changes to their product families and introduced new CPUs with higher performance and faster clocks. Density improvements at future nodes ensure both companies will be able to introduce CPUs with more cores than previous models, should they choose to do so. Will they be able to keep cranking the clocks up? That’s a very different question. The evidence thus far is not encouraging.