I pretty much just use my gravel bike on the road; being able to use joining tracks etc is nice but the comfort is the main thing.
I'm a new, heavy, rider in and the roads are in terrible condition so I started with a 700x28C road bike and found it pretty uncomfortable due to the high pressures, and promptly changed it to a 700x40C gravel bike which was noticeably better. Getting a new bike in the next month or so (hopefully) which is going to be the same 700x40C gravel bike. I don't really see the need for a dedicated road bike unless I find I need more speed or distance and the bike is holding me back.