One thing to note regarding cell drive strength with regard to Yosys, the Skywater PDK for the hd library has 437 different cells with various drive strengths. But the openlane "no_synth.cells" file contains 377 unique cell names that are not used by synthesis (the version of the file I have actually has 420 entries, but there a lot of duplicates). So only about 60 cells are actually used, unless perhaps the place-and-route stage is pulling in additional cell strengths, which I haven't investigated.