I applaud this, but...

That is true, but even then there can be mitigations your system can apply if it knows you're running in older hardware (for some definition of older). For example, a browser for older hardware will assume less available RAM, so the tradeoff memory vs CPU that leads to using several stages of JIT compilation when memory abounds may be more biased toward either baseline or interpreter only, or something in between (e.g. a threaded/context threading interpreter with a single instance for opcodes).
Also, considering many local applications are now just a browser running a web app, one mitigation may be not running a browser with a web app when you don't mean to. Some of the popular ones have alternatives (some better, some worse), e.g. for Discord there are a few native apps that are more sympathetic to hardware (although the one that worked the best for me is proprietary, it's not like the original is free software either).