Sorry for the delay. I am going to need to upgrade to the current version of TinyMCE in Cheetah.
The version in Cheetah is version 5.7.1 which is really not that old. Released 3 years ago.
But the current version is 7.5.1. It contains a lot of fixes and improvements including mobile improvements and fixes.
The changes however are significant and will require quite a bit of time to implement into Cheetah making sure all areas of Cheetah that use it continue to work properly.