1) RoR is slow, services, brake
No, the same order of performance with similar solutions (compare with frameworks in PHP and Python).
2) Not intended for high-loaded projects
The highload is a problem of architecture, not language.
3) RoR don't write a game server because of the slowness, there is a high latency and so forth ...
However, I hope you mean the Ruby (the language), not RoR (the framework).
Look in the direction of Java, if you want to solve such problems.
And advised us to : Python+Django
Performance Django on the level of RoR.
or Node.js !
It is impossible to compare with RoR, this is the solution for different tasks.