I did 2 A-levels and a BTEC. I can tell you that the content is pretty much equal, difficulty wise, between both BTEC and A Levels; A levels require slightly more detail than BTEC's however. The difference is in memory. With BTEC's, you don't need to remember anything, once you've completed an assignment on something, you never revisit it again, so don't need to memorize a lot. A levels obviously require you to memorize content years later for the exams.
With regards to University acceptance, it depends in the university. I got into a Russell group Uni with a BTEC instead of an A level. As far as I'm aware, Oxbridge are the only Uni's which don't except BTEC's as an equivalent to an A Level (and maybe medicine and veterinary courses?)
In my personal opinion, if you find an A Level too difficult and still need it, do a BTEC in it. BTEC's are much easier (if you work hard) because you only need to remember content from the last few weeks.