Got a message from the in game support people. Here’s what he said.
“I’d like to let you know that players are matched against others with roughly the same Trophies and rank as they are, so there is sadly no way to have only weaker opponents matched against you all the time. Please know, though, that the total power rating numbers you can see are merely speculative and should not be taken at heart.
Instead, you should look at which Dragon(s) will give you the most trouble and focus on getting rid of those first in wave 1. Then leave 1 Dragon alive (by making gem combinations that avoid the last Dragon) and try to heal back by using Dragons who have healing or heal-over-time ability. This will allow you to effectively get all your Dragons to max spirit before tackling another.”