As you have already read in this guide, the new 1.14 versions' general performance is much worse than in previous versions.
According to some reports and our own tests, the performance of 1.14 improves significantly if they have set a reduced render distance.
For this reason, all Vanilla 1.14+ servers have a reduced render distance. This cannot be changed, and there are no plans to change it.
If you still want to play with a normal render distance, we recommend switching to the PaperMC server software. After installing PaperMC, you can increase your render distance in the server.properties.
The reduced render distance is not what causes mob spawning issues in 1.14; more information about that here.