[Gravityloss]

Just as an example, a lot of companies are using jets on short haul flights where a turboprop would be a lot more fuel efficient. On short trips the speed difference doesn't mean much.

Again, there's some complex calculation about training, fleet diversity, flights per airframe per day etc.

If fuel is cheap, it makes sense to use the more fuel gulping plane because other costs are better. If fuel is expensive, maybe it then makes more sense to use more turboprops even though it means other complications.

Turbofan engine compression ratio and bypass ratio have been increased but we are nowhere near the limits of total aircraft efficiency.

Just as an example, Perlan II glider has glide ratio of 43. Of course, it's for a totally different use case and useless directly as an airline. But as comparison the most efficient airliner, the ATR turboprop has glide ratio of about 15.