I don't mind the Dubois trade for Washington.
You have to keep in mind where their team is in terms of their build. They are on the last dying gasp of Ovechkin's career and they don't have anything to really transition to.
Look at it this way, this trade is like Washington signing Dubois to a 3 year 3.25M contract because Kuemper was a sunk cost, and after those 3 years Ovechkin will be gone and they will embark on a long rebuild where the Dubois cap won't matter.
It's a win/win trade for both sides. LAK gets out of a big chunk of the Dubois contract and Washington gambles on adding a possible start, where if it doesn't workout, the opportunity cost cap wise is not very high.