I hate this for developers. I got to experience this first hand because I had a boss who thought like you.
Developers generally need to run a bunch of resource intensive tools to build the application in the first place, so an underpowered system will already be choking. It means their app will feel slow no matter what. So then when they run it and it's slow, they will shrug and say it's just slow because their system is slow.
There might be a case for specifically running testing on a slower machine, though.
There might be a case for specifically running testing on a slower machine, though.