A fresh world (i.e. not upgraded from 1.12.2) on a 1.13-pre8 vanilla server using the official server jar runs at 8-14 tps on my computer, where it would run the same world in singleplayer at 20. The same computer can also run a vanilla 1.12.2 server with a normal world at 20 tps without problems.
Steps:
Create a new world in 1.13-pre8, using default generation settings
Run debug profiler or observe the latest.log file
Exit and start the same world on a 1.13-pre8 server
Run debug profiler or observe the console
Optionally, compare results with a 1.12.2 server jar, with a similar world
The server should be skipping more ticks and having a hard time keeping up compared to the singleplayer integrated server.
Update for release 1.13: getting 19.98 tps when running on the server. While performance issues do still exist, this particular issue of disparity between performance of singleplayer servers vs the standalone jar appears to be resolved