Nice trip!
Makinaw is a good place for easy biking - good that you explored inland too. There is some fun (mild) mountain biking there too. Last time I rented a fat bike for the dirt trails, and enjoyed riding through busy areas on the shore with those super loud tires - they were effective at parting the crowds and certainly attention grabbing!
I do love that hike between upper and lower Tahquamenon Falls (especially the brewery/restaurant if you finish at the upper). I made the mistake of doing that in deep winter once and it was pretty post-holed (but beautiful).
Those Freighters go pretty darn fast when going down river (if you are at one of those points). As a life long gulf coast boy (once upon a time), I found it super odd to see seagulls so far inland. Not to mention the foreign concept of snow on beaches.
UP in general is not a great place to ride (as you noticed), although there are some pretty places - copper harbor is amazing - but incredibly far away from anything...