I'll have to see it in action to really get a strong opinion on it.... but I like the concept.
I would usually keep my ECR around 70-80% anyway so that my per-game rewards didn't drop too much, so I think this change will be a positive one for me. I'm sure I never got close to playing 50 games in one day, so I can't see myself spending DEC to play more games.
If I were, for some reason, were to buy the extra energy, I'd want to make sure I'd use it all since it seems expensive in Diamond League.
Overall though, you can see that the players who are earning the highest League rankings at the end of a season are playing thousands of games... and so we should start to see them limited to 1400(ish) games per season which means each win will be so much more important. I think that'll be a good change.