Due to its low cost, Flash could easily be played on turn one, allowing the combo to go off immediately
The reason it sees so much play is that it is doing two things that are well paired, both stalling the game and it is never a dead or even that weak of a card in any given matchup
Having both options at a playable rate in one card makes me very excited
Its at its best in a two-color deck, though three-color decks can make it work while your opponents have no idea what hit them
Its got an even higher ceiling in Commander, where its not too challenging to find the time to gain enough energy for this to start bringing back huge monsters
And there's a very important difference between previous, more linear archetypes and these wider archetypes: you know the shape of your strategy, but not exactly what goes in it