If OP is considered valuable by the organization and everyone is satisfied by their output then they are providing the value they are being paid for. If they feel they are overpaying OP for for the output he is providing then they would PIP him or at the very least say something. OP though has received promotions so they must feel he is doing a good job.
Yes - it's perfectly fine if OP isn't stressed or not doing a lot - if their 2-hour genius contributions are worth $200K to the company that's perfectly fine.
This however, is probably not the case.
The common case is that due to lack of proper oversight and bloat, people just coast and do nothing.
It's incredibly hard to have 'true oversight' in software, which frankly is 'just fine' if everyone does their jobs properly.
But if the cost of 'little oversight' is that slowly but surely 'nobody is doing anything', it's not going to work out now, is it?
That's obviously for the company to judge. If they continue to pay him and promote him, why is the takeaway that he is committing fraud by not working an arbitrary 40 hours a week?
I for the most part agree with you. Its probably not 100% on the up and up but a very large group of us do it.
If everyone started working the full 8 hours then deadlines would be hit in half time or less. What would prevent the company from then deciding that they have to many engineers and laying off 30% of the workforce? It would save them a ton and they are still getting their goals accomplished in the same time frame as before. I feel like everyone coasting allows 25% of software engineering roles to exist. Don't get me wrong I am not saying we are angels helping our fellow man, quite the opposite; just an interesting thought experiment.