You are right most developers are not very good at that. I think it’s important to stress that this goes both ways. You should not cut your margins if you take longer, but I also think it is a little unethical to bill more hours than one spends no? At least if you have a clear agreement to bill by the hour.
The way to ethically handle this is to have a clear and contractual minimum number of billed hours in a day. That will get you paid well for built in efficiencies like OP mentioned, and keep you paid fairly on more substantial change requests.
What you’re saying is that it’s inherently unethical (to yourself!) to accept hourly billing for work the whole point of which is exponential automation.
