I'd say branching out a little is never a bad thing, especially as there usually can be a way to apply the things you learn from one subject to another. Figure drawing can help you with anatomy, which you can then apply to your creature. And since the environment where a lifeform lives will influence how that lifeform looks, then studying that could also help your designs.
Also, I think that if you eventually want to work in a studio, being versatile is probably a good idea as you'll most likely going to be asked to work on multiple things and not just creature design. And if you're aiming for creature illustration, then the versatilty may be a bit less important, but I'd still give a focus towards environments as you'll probably want to set your creatures in interesting and convincing habitat.
With that said, if what you really want to do is creature design, I'd probably keep that as my main focus. Just remember that new knowledge is never useless
I hope this helps and keep up the good work! I really like that creature you've posted.