I concur. Using high level (like 14 and 15) champs or any dragon against opponents less than level 6 can result in early losses (remember the disposable Fire strategy against champs, it can work in reverse). Some people I've seen use the same dragon throughout most tourneys which I don't think is a good idea either because there are others that would be more effective.
For me I use color advantages when choosing dragons and never go on a whim or whatever dragon I feel like using. This is how I win tourneys on a fast pace and haven't lost out on a tourney since early 2015. Sometimes when facing champions I look at the color of the dragon itself and and use a dragon that would beat that color just for fun.