I honestly think parts make the OT more flexible than the digis…
They allow you to make multiple patterns that all share the same kit (part). Most of the time a part is worthy of using multiple patterns. One pattern is usually not enough to exploit the selected sounds and such that a part has defined. It becomes very nice to make a progression of patterns that all share the same sounds. This has a major, major benefit to live tweaking. If you say close the filter of a track on pattern one and then switch to pattern two, if it’s using the same part the filter will still be closed on pattern two instead of snapping to whatever it’s saved position is. Basically they allow for live improv tweaking over a progression of patterns…
I think what throws a lot of people off is that they think they should try to use parts by changing them on a pattern with the sequencer going. Parts are very much like drum machine kits, they’re main use is to link them to a pattern once and then forget about it. When you switch patterns the OT will also switch parts to whichever one you have linked to that pattern.
Another thing that throws people off is that there are only 4 per bank instead of 16. It’s really not that bad it just means for every 16 patterns you have 4 kits at your disposal. This is why a lot of people use patterns 1-4 linked to part1, 5-8 part2, 9-12 part3, 13-16 part 4. This allows you to make a progression of 4 patterns that share the same part and allow for improv tweaking, and then a new part for the next 4, etc…
All in all the OT has 64 parts. I do not recommend this but if you really wanted you could assign pattern1 to part1, pattern2 part2, pattern3 part3, pattern4 part4, for every bank. If you do this and simply ignore patterns 5-16 of every bank, the OT would behave just like the digis. You’d have 64 patterns each linked to their own part and you’d just use patterns 1-4 of every bank…