Firstly, losing 4G coverage isn’t an issue where I use my phone. I don’t live in a third world country like the US. Despite this my iPhone will randomly decide

Firstly, losing 4G coverage isn’t an issue where I use my phone. I don’t live in a third world country like the US. Despite this my iPhone will randomly decide to downgrade to 3G. As to what the phone should do when going outside an 4G coverage area when being in “4G only” mode is nothing. It should just aggressively try to reconnect. A discrete icon about 3G network availability should be shown. A press on the 3G icon would enable temporary 3G roaming. The underlying problem is that Apple handles roaming between 2G/3G/4G networks poorly. I could wish Apple would do it better, but that’s like wishing for an unicorn. Hence my strong leanings toward jailbreaing.