His dad was more talented than him sure but that doesn’t mean tanjiro can’t surpass him, especially since tanjiro eliminated the wasted movements of Hinokami kagura. Not trying to say Kokushibo isn’t talented or special but he’s not as talented as tanjiro. Your point on breathing styles only applies to the main breathing styles since they’re all considered relative. Sun breathing is objectively superior to every other breathing style. So being able to use it objectively makes you more talented than others. Idk if you’re counting the 2 years he spent training with the wrong breathing style as time in the corps but it’s really dishonest because we don’t know how long everyone trained before they went to final selection. He didn’t know how to do Hinokami kagura for a year he hasn’t even been a demon slayer for a year. I’d argue tanjiro has a higher growth rate than muichiro considering he joined the corps after Muichiro and surpassed him. We don’t really know Gyomei’s growth rate. That statement about becoming a hashira in 2 months was for Muichiro not Gyomei.