Rytm is built along the lines of all the other machines except the OT.
Parts were quite a controversial concept when introduced. A lot of people didn’t like the fact that each Bank only had access to 4 Parts (Kits)
All the other machines tie a Pattern to a Kit, (ok MD doesn’t in Classic mode), so the Kit is instantly recalled with the Pattern. There’s is nothing to stop you loading a different kit on the fly tho. Remember the Pattern will load the last associated Kit, (unless you recall a Project). You could also have 2 (or more) identical Patterns each associated with a different Kit if you wish.