I can definitely hear you on the i9 MBP 16-inch model. For all the extra power it offered, the i9 model did "chew through" more battery power than the comparable i7 models. The fan tends to spin up more often than I'd like on the i9 models. I also owned a 2018 MacBook Pro 15-inch i9 model, and my experience was similar. Rather poor battery life, and almost not worth the extra power you're supposedly getting, at least not for my use case.The last time I went all out and bought a future proof machine was Feb 2020 when I bought a i9 16” MBP, 32gb ram, 5500m 8gb. Man that one really bit me in the ass hard. All that extra power made it hot/loud and chewed through the battery. Though I did like 32gb of ram for adobe stuff and would use it all. I have used 16gb ram in the past and hit the limitations.
You'd think that having a more expensive Intel processor on a Mac would make the whole thing more energy-efficient, but my experience has been the opposite. Probably one of the best Intel Macs I've owned in terms of battery life has been the MacBook Air 2018 i5 model. I've also owned an 2020 i7 model MacBook Air, but for all the supposed performance benefits that the i7 offers, the i5 just seemed more power efficient overall, at least for what I was doing.