We had some Nordic skiers in our collegiate cross country team. They has zero top end but they could go all day at threshold with their 70+ VO2’s. They had the cool ability to rapidly recover with any dip in effort. The cycling equivalent would be that they had the ability to recover nearly instantaneously if they came 1-2% below a pro level FTP.
There used to be a weekly training ride that a couple of guys that were on the Olympic Nordic combined team would come out to. Their level of fitness was incredible and they would blow the doors off the local cat 1-2’s when thing things heated up. It’s just a different level. My opinion is that you can only get so fit just riding a bike and that you need to do other modalities to actually achieve your potential .