Intel's stock cooler was fine when their cpu's were only pushing 3 to 3.6ghz. But when they started pushing past 4.0ghz boost, the thermals definitely hindered sustained boost clocks. Intel's stock cooler is only rated for 73watts TDP. We know that youtube reviewers recently discovered maybe last year that most motherboards will do a factory overclock of Intel CPU's. You have to use intel's utility app to lock it to the actual rated TDP. So if you buy a processor with a 65watt tdp and the cooler is rated for 73watts, and there's potentially a factory overclock on the cpu, you can see the issue here. You can see Gamer's Nexus do a little write up about it:
https://www.gamersnexus.net/guides/3385-cheating-or-optimized-z390-motherboard-bclk-comparison
But we also have to keep in mind that Intel only rates TDP at BASE CLOCKS.
The problem with the 2600 is that AMD decided to downgrade from the Wrath Spire(95w tdp) which came with my Ryzen 1600, and give people the Wraith Stealth(65w tdp) with the Ryzen 2600. Which is no better than Intel's stock cooler. You'll be oscillating between turbo and base clocks very often.
With either CPU with the stock cooler, just count on the base clock as your standard. Any turbo boost clock you get, just consider it a bonus until you can purchase a decent cooler. I have the Cooler Master Hyper EVO 212 on my server and it's a very good cpu for the money($35). Worlds above any stock cooler.
If you can swing the extra $20 for the Ryzen 2600x right now, it's well worth it for the better 95w tdp cooler and the extra clock speed of the chip itself.