I mean flash is a utility for a different scenario than the grenade, you can use the flash for all kinds of play. For creating a opening, holding a spot, changing you spot, helps while defusing, helps attacking sites easier, causes Ts to move back while pushing. The flash can be used by both the ones who wants to get the entry frags or the one who wants to stay away from a fight, so can the grenade but it was made to make attacking easier.