Qtractor and lmms (via wine?) can load (some?) vst's (important feature to use only one midi port), but can not construct them.
Using Ctrlr, you can construct midi editors for nearly any midi hardware (sequencer, mixer, sampler., drummachine..) both as a standalone editor or as a vst-plugin. And this in different ways for every single machine (library, patch editor, mixer, sysex dump organiser ...). Ctrlr can output this drivers also as a xml file.
So Ctrlr can be a very useful auxiliary program for such software as qtractor , lmms or Rosegarden.
It features also the lua scripting language that still enhances its use in a steep way.
Nevertheless you are right to favour software used by many users.
And it is really a pity it isn't Qt centered. But I'm not aware of an alternative in linux