It is actually a problem that my friend has. We tried doing same climb on Rouvy: around 5% grade, I rode on a medium gear (34 front, 18 rear), my friend was on his easiest gear (34 front, 32 rear). I was producing 130W with cadence 80 maintaining low speed, around 8kph. My friend on the lightest gear was incapable of continuing with me, because he had to produce more than 300W with a very low cadence just to keep up with me. Strange, as we both have Wahoo Kickr Core, same firmware, same Rouvy version.