I haven't used Hydrogen yet but it seems to be much more than just a drum synth/simulator, such as the ones you referenced as comparison (Studio Drummer, EZDrummer, etc).

Drum machines can mix and compose a variety to samples and synth sounds, these samples can be drum kit sounds but it's not necessary. So you likely only sampled a limited portion of the functionality.

You could also always purchase high quality drum samples and use it with this OSS programs if the built in library sucks. From experience, you could accomplish quite a bit with relatively simple drum machines.

The synth products on the other hand were the thing that was complex and needs to be high quality. Which is likely what you were looking for a drum simulation.