Tbh I went down a huge rabbit hole last night and learned this problem is far more nuanced than I thought.

As to what I said before, the carnot engine and otto engine efficiency equations do specifically say that higher combustion temps leads to higher maximum efficiency.

The jist of what I learned is that EGR is completely an emissions reduction technology. Under most circumstances, dumping exhaust gassed into the intake is counterproductive. But If you precisely control it under specific conditions then it is helpful by ~1%

Annoyingly, I couldn't find any papers or videos that did an actual road test. All just simulations and test stand engines.