Originally Posted by fstrnu

And FTP (along with NP, TSS, TSB and other silly derivatives) is terrible indicator of anything other than test performance. Two riders with the same FTP can have vastly different endurance, load tolerance, VO2 max and so on. The list is too long to cover in a forum post. Athletes are more different than they are the same and the only way for you to discover what you need is to monitor how your body is responding to training, using tools such as the internal to external load ratio, cardiac drift, HR vs cardiac drift, etc.

ERG training fixed power under controlled conditions makes these measures even more reliable.

Use EF for performance and if it's improving then you are doing something right and also need to progress your training.