My question is about 'writing experience' and how that helps you in the game of getting published.
I understand that for an unknown writer to be picked up by a publisher their work would have to be brilliant, or they would just have to send their manuscript to the right place at the right time (i.e. they're lucky). But there are thousands of submissions each year that are just 'very good' which means, although they may be publishing worthy, they may not necessarily be picked up. Some suggestions to help writers in the 'very good' range are to get short stories or articles published, win writing competitions etc.
My passion is in writing novels where I have the time and word count to develop a character and present their journey to my heart's content. I struggle to write a good short story and I don't believe this is where my talent lies. However, I would be more than happy to pursue this if it does indeed help in the long run. Therefore my question is this: in your opinion, are agents or publishers really likely to give an unknown writer more of a chance if their query letter shows they have published some short stories or won one of the many random competitions?
In short: no. At least, I don't discount writers if they haven't had short stories published or had short stories win competitions. Short stories can be a very good discipline if they appeal to you - the same way that writing poetry can be a very good discipline for writing novels if poetry is your thang - but I'm struggling to think of the last writer I took on who had written any short stories at all ... Word search ... Search fail.
If novels are what you love writing, then stick to what you love. You may never get published - statistically, most novelists won't - but I can guarantee this: you will never ever get published if you don't love the form you're writing in. If you start writing short stories because you think they'll be helpful and your heart's not really in it, it will show in your writing. If you write a screenplay because you think it'd be cool but the screenplay form is something you really struggle with, it will show in your writing.
So stick to the novels. Maybe enter them in some comps; maybe apply for the odd development program or mentorship. That stuff does look good in your bio simply because it shows that you enjoy the writing process. And don't forget to have fun.