Replace the timed fuse with a proximity fuse: arm after a second or two in the "air" and then, upon a target entering the blast radius, as soon as the distance to that target starts increasing rather than decreasing, go boom! De-arm after coming to rest to prevent them from being used as mines. You'd still need to compensate for differences in gravity, but they'd be a lot more useful than the nigh impossible to aim grenades we have now. You'd still be able to bounce them off of walls, too, unlike with an impact fuse.
Or... replace the frag and EMP grenades with self-guided drones that travel in whatever direction you launched them in and, once a target enters its "activation range", have it home in and detonate. We've already got autonomous skimmer drones with the green light to use deadly force, so there is in-universe precedent for the technology.