I agree but would add that within the codebase there are also vastly different experiences. The search ads serving stack for example is phenomenal, it is >10 ye

I agree but would add that within the codebase there are also vastly different experiences. The search ads serving stack for example is phenomenal, it is >10 years old, very complex and gets contributions from hundreds of engineers every week, yet it is quite easy to understand what is going on anywhere and it has great performance. But I also had to work with other code which had been through 3 rewrites, none of which had ever been totally completed, so there were overlapping paradigms everywhere and working with it was just a nightmare. Tests never caught anything leading to several post mortems.