Quest brackets should be based on Might

Actually I've even seen TH 18's with 500mil might

 

Exactly. Nor are allies. Just some biome research won't magically make up for 300% more ally bonus or tier 7 dragons these guys have

 

They have a limit to the number of allies they can have as well. You would just have to invest some more gold in some better allies and you will see your % go up too.
If you are 30mil at 18, you probably went to 18 too soon. I was at least 100M before I went up to 18 if not more. If you can't hit the max level monsters at your TH level, it's not a good idea to go further until you can. Things will only continue to get harder. By moving up to a higher townhall, you are going to be pushed ahead. Imagine you competing with a TH25 who rushed TH and has low might but has 4 marches and researched T4 and you're still stuck with guards. Would that be fair? There are limits to what you can do at each TH, and that's why they break it up by TH rather than by might. Might is not a full indicator of what you can do. You can have your research in many different areas in the tree. Slow down building your Town Hall levels up so you can compete with those who are in your bracket. You don't have to move ahead. Don't worry about trying to be the top TH the fastest. Things only get harder and harder as you go up. The point requirements in your brackets are based on what you're supposed to be able to do. So catch up on that before you go ahead. If you go to 19 as you are now, you'll be in for a big surprise...and not a good one.