This may be how it was intended but I thought I would put my two cents in as I know I would enjoy the game a whole lot more if this was changed.
There sometimes seems to be some kind of either lag or issue when I am using my primary skill (Left mouse button (LMB)), and then quickly try to use my secondary ability (Right mouse button (RMB)). I have to usually click the RMB several times before it starts to use the ability.
If the transition from LMB ability to RMB ability was instantaneous and occurred right when I started clicking RMB, In my opinion the game would play much smoother and be much more enjoyable.
Otherwise great job gearbox!!