To get rid of the excessive brush strokes you will need to do some sanding. This is problematic as the new paint will get gooey when sanded. Rolling when properly done can produce a very even coat and a nice effect.
You should properly condition your paint for brushing and rolling. See this article about <a href="https://www.house-painting-info.com/paint-additives.html">Paint Additives</a>.
Using the correct roller is also important. Wooster has a nice 4 inch flocked foam roller for their Jumbo Koter roller frames. It produces a very nice finish. Try to use something similar.
A better paint will help. I'm not a fan of Valspar. Sherwin Williams Super Paint works very well.