As I read through the comments, one thing that is not mentioned (per se) is a scale of usefulness (for lack of a better word) of a bike route. I’ll try to explain what I’m speaking of (and use some examples local to me) …

Usefulness level 1 - protected bike route. No competing motorized vehicles. Paved/finished.

Usefulness level 2 - semi-protected, but legal, bike route. Has competing motorized vehicles, but a portion (e.g. shoulder) is available to bike riders. Paved/finished.

Usefulness level 3 - unprotected, but legal, bike route. Has competing motorized vehicles, bikes are relegated to the same travel lane as the motor vehicles. Paved/finished.

Usefulness level 4 - unprotected, but legal, bike route. Has competing motorized vehicles. Unfinished, and therefore there are no lanes per se, but traffic volume may be low. Surface subject to degradation during periods of rain/snow.

The last one may be less common in most places, but represents about 2/3 of the local roads in my area. Over the past 3 days, I’ve measured 200mm of rain. I won’t go near any of those (on a bike) for at least a week.

These levels are orthogonal to some of the other tags, but they allow a simplicity of how a routing algorithm may select various trails/streets/roads/etc. There may be other valid levels I’m not aware of.