I would suggest using the symbols you developed for character types (assassin, tank, etc) at the top of the page for sorting, rather than a drop down menus. Drop downs are so soviet era.
Consistency is important. On the Champion Collection page the Owned, Available and All filter is in a drop down, while the Alphabetical, Mastery and Recently Played are buttons... Why are they not all buttons?
Also, instead of the drop downs in load out selection, how about a load out button that takes you to a load out page where you can see your runes and masteries easily and select them for the match.
The whole client is mostly button based, stick to that.