Commuting is like any other cycling other than the length being fixed and often being shorter than a weekend ride. So, it will certainly get you very fit if you apply all the standard bike fitness tricks.
I personally fartlek it on my commute .. a long hill is an FTP interval, a short hill is a HIIT, etc. Since my commute is only 6 miles it is ideally suited for more intense intervals, and it has 500 feet of hills for good fartlek-ing. I do my longer zone 2 rides on the weekends. I usually don’t wear my heart monitor on my commute but when I do it is 10bps over my weekend rides on average.