Under the old 25 gems rush: I could play 24 games (assuming I lose them all) open 24 common crates (this will never happen because I have never received 24 common crates in a row) for about 12 cards each, I get about 288 cards for 600 diamonds. Assuming each game is around 3 minutes, it's a little over an hour of play.
Under the new gems rush: You are asking me to not rush, wait 3 hours for each crate. If you opened up a crate every 3 hours, you can open 8 crates in a day. It would take you 3 days to open 24 crates. Oh, and you want me to wait until the vault gets 300 cards to open for 600 gems that I could have spent in an hour for more cards?
How exactly is "this a MASSIVE improvement to crates?"