the support section is break down into forum part where people discuss about problems they are having with themes and plugins
I think most of us here considered the "support" section of a site to be something else... utility pages, as aakk9999p suggested, pages like
"about us, contact us, FAQ page, privacy, ToS pages" etc.
If problems are truly being discussed and resolved, then the discussion pages, which you describe as "support", are kind of like this thread in this forum... where we try to resolve various issues. In WebmasterWorld's case, we're not selling any products, so our support tends to be far ranging.
I'm guessing that you are selling the products that you support, and the discussions ought to be popular with your users. If they aren't as popular as the link juice they consume, then you've got a structural problem, or a moderation problem. Or maybe the rules of your forum aren't encouraging good discussion. We don't offer public site reviews here for a bunch of reasons. One of them is that such discussions are generally not self-contained... they often don't contain a statement of the problem and its resolution... just a "hey, look at this and tell me what's wrong", and that's not really productive discussion. Though that may be what your users need, it doesn't make for content that is of general interest.
so every problem creates one different page. so it's kind of big
Possibly, you should look at the structure here on WebmasterWorld, and at the structure of support forums on other tech product sites. If I understand you correctly, it sounds like your site structure is too flat. I'm thinking that though each problem creates a different page, by sufficiently categorizing these pages into prescribed areas on your site, you could limit their sprawl over your interface.
I think you understand that you shouldn't link to everything from home. Go deeper with discussion material that doesn't attract an audience. Ultimately, the pages that have gotten links from elsewhere will survive in the serps, and the rest won't be draining link juice from other pages.
It sounds almost as if you've got this set up on blog software, so you're getting too many recent posts on your home page. If that's the case, maybe you've got to rethink the site structure.