I’ve had a very similar experience.
I clock about 700hrs annually. All my lower duration power numbers, are what they are. They don’t move much. However, on long rides or races I’m far stronger at the end. Particularly in comparison to riders who average less training.
It’s actually quite noticeable. I’m the same as everybody, until about the 3hr mark. It’s usually about then, that the people I’m racing or riding with, noticeably fatigue. It’s a durability you don’t get from lower annual volume. Additionally, I consume vastly higher carbs than most riders, both in pivotal training sessions and racing.
Combined, it’s a noticeable difference.
Is it worth training for this difference. Probably not. I think many could be very close on half the volume. Say 350hrs a year.
High training volume, say over 600hrs a year, is only necessary if you’re racing long durations and are highly competitive. Meaning, it’s incredibly important to you or it means the difference between winning or losing. If so, have at it.
For most folks, doubling the volume from 350 to 700hrs, absolutely will not double your performance. Not even close. In fact, it’s difficult to even measure. Durability is hard to quantify in metrics. You can feel it, in relation to others more than simply looking at power numbers.
Perspective.
If you’re having to do 700hrs of annual training to get to 4.5w/kg. You’re either a little too old, late to the sport, or an average or slow responder. Genetics absolutely matter. Fast responders to endurance training will improve well beyond two times faster than average responders.
It’s important to be realistic. What are your realistic expectations?
Running a large cycling club and having friends who coach riders from learners to professionals, has given me a far more realistic and healthy relationship with goals. Both personally and in regards to other athletes.
I’ve discovered that w/kg targets are the absolute worst possible metrics to focus on, long term. They are close to irrelevant. Forums like these. Zwift and a million websites have most cyclists almost obsessed with their FTP and w/kg.
I get it. It’s fun and gives us something to aim at. However, it’s an illusion.
If you want to improve as a cyclist focus on PERFORMANCE. I don’t care what your supposed w/kg is. W/kg does not win races. Humans win races. Racers win races.
Racers with incredible skills, powerful sprints, next level bike handling etc etc. Thinking you are somehow a great cyclist because you hit some arbitrary mass vs power equation is short sighted.
Yes, of course we need to have a level of fitness to join the party. However, rarely is that single metric going to determine the result. Maybe, if you’re strictly a competitive hill climber, obsess away…
Obviously, we all like different things. Different music, different food. We all have different drivers, be that racing, social interaction or simply our own personal fitness goals.
However, based on watching a large volume of riders come in and out of the sport. The faster you learn that cycling is not just w/kg, the faster you’ll improve. The faster you’ll enjoy other aspects of the sport. The faster you’ll make new friends and experience new events.
Leave the w/kg fixation to the professionals.
Face it folks, if you ain’t over 6, you’re pretty crap anyway