I think if you are struggling with biology at AS, then taking it to A2 could cause more stress and you would have to be willing to put in extra effort to achieve, also if you did decide to continue with bio then I wouldn't advise taking up another AS level as this would be added work. :/
But really, biology is unlikely to open up many more doors simply because you are not taking any other science based a-levels and any university degrees in the science domain usually ask for more than one science based a-level.
As for Media being seen as a 'soft subject', that is just misconception as Universities understand that all a-levels require a high standard of work and accept it just the same as any other a-level course.
Really it depends on whether your love of biology would enable you to put in the extra effort and do well. If you really wanted to take up another AS level during A2s then I would drop Biology, but thats just me.