@Moepi, sure, that would make sense. I've added an issue to track it:
https://github.com/EsotericSoftware/spine-editor/issues/686

If space+LMB would be better for you, you could customize the hotkeys to do that, just set Pan Drag: SPACE in your hotkeys.txt file. There is also Pan Move which would pan when you hold the key and move the mouse (or pen), without needing LMB.

@Moepi, actually we already have a setting so MMB can pan:
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