That’s the point: if you’re not customizing Blink, you’re not changing the huge influence which Google has over de facto web standards. If you want to make more than simple customizations you need a significant commitment just to keep pace with the upstream – Microsoft can afford that, Samsung can, etc. but it’s not clear that Brave or Opera can.
I just discovered Goanna on Wikipedia, a fork of the Gecko engine, presumably with relatively thin resources. Don't know how well it compares to mainstream engines though. [0]
I suppose the short version is that the workload is a function of the goals.
[0] https://en.wikipedia.org/wiki/Goanna_(software)