You want a spare tire in case you need it.
Having said that I'm reminded of our 2000 Jeep Cherokee Sport sitting in the carport with 133,000 miles on it and a nice/pretty spare tire that has never been out from under the cover on the side of the luggage compartment, let alone on the road. Same for the 2005 Silverado 4WD. That spare was on under the truck but I moved it to the bed (inside a camper shell) to keep the salt off it during those winter time trips to WV. Neglected thing has never been out of the bed except when I was cleaning up prior to a camping trip and wanted to wash the bed liner out thoroughly.
The practice of smaller spares than the four on the road goes back (at least) to the early 80's. My 83 Z28 has a small tire in the spare tire compartment. My 86 IROC has a really weird looking spare. Looks like as wide/flat wheel barrow tire. You pull it out, knowing it will never match those wide 16" tires/rims and hook up the little bottle that was stored with it and next thing you know it unfolds, fills up and fits (size wise) just right. You drive it to a tire repair shop, they put a plug/patch on the flat tire, fill it up and put it on the IROC and then let the "air" out of the spare and the darn thing collapses back to it's original shape and goes right back into the spare storage area. Some of those did come with aluminum rims, but the are still smaller than the running rims/wheels. My black IROC has the black painted steel spare tire rim and the red one has an aluminum spare tire rim.
Don't sweat the size of the rim, it's the overall diameter and tire pressure that will get you off the side of the road (and a jack and lug nut wrench, and the knowledge of how to actually change a flat tire - don't laugh, we all know folks out there who would be standing on the side of the road looking at the flat and wondering what to do until they froze to death or got hit by another vehicle.)