In most cases it's not. Quality posts are determined by the content of the post itself, irrespective of how long the post is or not.

I've read a good number of posts that were quite lengthy but had nothing to offer overall and I've read posts that were 3minute reads but had so much value that I had to RESTEEM and tell people about it.

Focus more on creating posts that have relevant content in them and I guarantee your posts will be referred to as quality content.