So I dont think it's a useless degree far from it. But you are right in that I suspect a lot of industry biomedical engineering companies hire: mech-eng, EEE. I think it's important to note a couple key things:
1) There arent that many BioEng grads, so companies need to look wider (wider net means you can access more talent)
2) Lots of what these companies do will work on specific areas within the system (i.e. you dont need to be an expert on the full system to work on one area, and this is actually more true at graduate level roles)
3) You can still mold your degree to the job market, just because it's advertised as a mech engineering role in Bio-engineering doesnt mean you can't apply, you can look to leverage your current skills and expertise to the full job advert. (it's pretty normal for engineers to apply to a wide number of industries regardless of what type of engineering they have at UG.
4) If you want to you could see if you'd be eligible for a Mechanical or electrical MSc then you could apply to companies with a Biomedical BEng + Mech/EEE MSc (and you can offer the best of both worlds)