Dennis 12mbs is not a bad speed on 4g especially if you are rural. To put it simply as you move away from the tower your signal degrades. Rural towers can sometimes be as far as 20 miles apart in small towns if its flat terrain. While different versions of 4G claim speeds up to 150mb or more its not the backhaul that is the limiting factor. The issue is the amount of frequency owned by the provider at that location. Then that frequency is shared between all the customers using that tower at same time. When you have more frequency you can do things to improve speed but it requires higher end phones to take advantage of those things. IE your phone can make multiple connections to the same tower on different frequencies and or multiple connections to the tower instead of 1 all at the same time increasing your speed. 5g you will not see great speed increases in rural areas unless the provide adds frequency. The very high frequency stuff is very short distance and will be used in metropolitan areas to provide very high speeds but will require you to be very close to their equipment.
The 600mhz auctions that recently completed used to be the Analog TV range. The reason they Gov went digital was to get all the frequency and sell it to providers. If your provider adds 600 to the tower near you it could add additional speed by the means I spoke about above. The lower the number the farther a signal will travel and the better it will penetrate.
We have LTE on our phones, but have a local wireless provider for internet service. Our antenna has almost 20 miles between the transmitter and our receiver. I have to use a pretty good set of binoculars to see the grain elevator that it's mounted on.
12 mbs gets us by but thats on a good day. Like you explained, users can cause a loss of speed across the bandwidth. We see slower speeds around late afternoon when folks get off work. It's just part of rural living. I wouldn't trade it for anything.