No one hyped Jennings, didn't even hear of him until I found out he was playing the SA tests lol.
Ballance more to do with the fact he has an incredible domestic record. Especially in a country where domestic averages tend to be on the low side. He also tasted early success.
England overhyped their players in the past, they accepted bowling mediocrity especially. That's changed now mid 30 bowling averages aren't accepted anymore.
I think England should stick with the guys that average high 40s/50 in domestic. It's clearly very hard to average that in England domestic, there must be something special about you to do so. Time and time again they go and try out some new guy who averages mid 30s with the bat and a stellar recent season. It usually doesn't work out, in fact I struggle to remember a time it's worked out.
If you look at the guys performing in the England team, it's Root, Cook, Bairstow, all who have done well in domestic (and good overall domestic records). Why I'm tempted to give Ballance a few more goes albeit down the order.