Recently built up a Salsa Journeyer with Deore M5100 and earlier a Diamondback with M6100 - both with Sunshine cassette before switching to SRAM NX and Shimano XT. Because the shifting was terrible. While it improved with SRAM cassettes, I can never get the same feeling as my road groupset - Ultegra/105 or even Tiagra 4700 all of which are positively smoother shifting with almost no "bad" spots. The Ultegra especially is near perfect despite being years old at this point.
On the other hand my M5/6100 groups always have 2 or 3 indexing problems which I can't seem to get rid of. I tried changing their default shifters to SLX and XT (M8100) but that didn't help. So apparently shifters aren't the problem.
Should I just assume that jumps between cogs are much larger on MTB compared to road cassette causing the inferior shifting performance? Or is there a trick to index mtb groups which is different from road groups? I read that you should let your brand new chain and cassette run in for some period to settle them down with each other which I did. The M6100 has about 200 miles while the M5100 has close to 300 but shifting hasn't improved. Do they need even longer run in period? I'm baffled.