Hey I want you to know I've been in your shoes and you're not alone. A lot of runners, both amateurs and pros, struggle with this at some point in their career. I think the same intrinsic drive that makes us good runners can also contribute to some obsessive habits. I can only really speak to my experience but hopefully this helps you in some way.
I was in a really bad spot (6’3” 140lbs), and I found I needed to take a step back from racing. I eliminated all future race plans, which seems scary, but if you are actively training for something then that thought of “I need to be lighter if I want to race well” will be hard to shake. You’ll feel cramped for time and feel like you need to take shortcuts to lose pounds fast. So I scrapped all plans and just focused on building base. Starting over.
Secondly, I got rid of anything that helped me obsess about my weight. My scale, my calorie counting apps, etc - I got rid of them. If I had no way to track it, it was harder to worry about it.
Third, I looked at some of my heroes like Chris Solinsky, Craig Motrom, and Desi Linden. All non-traditional body types, yet some of the absolute best runners out there. For every 120lbs guy with the traditional “ideal body type” there’s someone with a BMI of 21 or 22 or higher absolutely crushing it. Andrew Wheating was a fucking unit and still one of the best 1500m runners around. Even Pre was a stockier, thicker runner, and that 5000m in 72’ was amazing. Alan Webb… ‘nuff said. The fact is consistency and recovery matters so much more than weight. If you aren’t eating enough then you aren’t recovering well and that will slow you down so much more than an extra pound or two. Your ideal power to weight ratio will not be the same as the guy or girl toeing the line next to you, and so don’t worry about looking like the guy next to you.
I ran my college PRs at 165 pounds running 60-70mpw. I ran slower at 140lbs running 80-90mpw. I am running significantly faster now at 175-180lbs running 45-55mpw (14:4x 5k, 30:4x 10k. I look like a fucking jav thrower and yet i’m running great for me so don’t worry about what other people are racing it. If you stay consistent and do the right work, your body will find what's most efficient for it.
PS: it would be so hard to eat too much if you’re running 75mpw.