As you have already read in this guide, the general performance of the new 1.14 versions is much worse than in previous versions.
According to some reports and our own tests, the performance of 1.14 improves a lot 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 to switch to the PaperMC server software.
The reduced render distance is not the cause why the mob spawning is broken on 1.14, more information about that here.