In my mid 20s I climbed fast. Won a couple hill climbs, did well at a lot of steep races. My bike was 53/39 and 11-23 most of the time. I had a "climbing" cog at 12-25 I'd occasionally run, like if it was crazy steep. I borrowed a 12-27 that everyone was talking about and hated it. Too low.
Fast forward 15 years. I have gained one pound I think. But boy have I lost some muscle and lungs. My road bike is 50/34 and 12-30. It's very low and excellent climbing. I don't think I'd want to go lower for a road bike.
My gravel is 40x42 at the lowest but when you factor in much bigger tires, it's only a few gear inches less than the road bike. I'd love to try 36x42 with a 10 tooth high cog. It's very cost prohibitive on my build to do that though.
My vintage Spectrum has 53/42 and 13-24 6 speed. I'm not sure it was ever considered a climber, but I use every gear on every ride. That's pretty cool.
I have a local monster, 3500' in 8 miles. 3000 in the first 5. I've been up it with a mountain bike at 20 GI, a gravel at 26GI, and road at 30GI. The speed is approximately 8 minutes faster with each bike. Probably due to the weight, 18, 22, and 26 lbs, not the gearing.