Road bike vs fancy road bike won't make a massive difference in commute times. My gravel bike is my main commuter (with road tyres), but as the weather is really nice right now, I'm using my road bike, which has faster tyres. Difference in commute times is maybe a minute or 2. Earlier this year, when weather allowed, I was also using my TT bike for commuting (TTs after work as well as just getting time on the bike prepping for the 100 mile TTs I had coming up). Again, there was maybe a minute over my road bike. My commutes are generally easy recovery rides. Once a week I have a workout from my coach that I do on my way home. Occasionally, if I'm feeling it, I will just smash my commute- this is where I make any gains in time. And they can be significant (8-10 minutes).