It’s marines if you’re a bio player. Cyclones or vikings (± mines) if you go mech.
But guess what, with proposed buff, stimmed marines (4.72 speed) wouldn’t be able to catch speed rays (5.11 speed). Do you see the issue ? Not to mention, even before introducing fluxvanes, the aerial nature of the VRs still allowed them to escape by using dead spaces. Now they’d be impossible to catch by a terran, and could be inefficiently catched by suicidal blink stalkers/phoenixes as a protoss. 
I 'm not sure about that. I mean, in almost every high level PvZ SG opener I saw, the limiting factor in harass performance wasn’t the oracle’s energy, but its tanking against queens and spores. And if you killed 3 drones in a pass, it would already be a good performance.
Anyway, even if reducing the pulsar’s beam to 10 was to much, you could go for 15, or 15+ a slight decrease in oracles’ starting energy (so that they don’t hit faster once produce, but can activate more often later). Or tweak the cost, IDK. Just don’t break the game by making the VR outspeed 95% of its counters…
That applies to midgame.
In early game, IMO nobody make VRs because your want to kill drones (-> oracles/phoenixes), unless roaches/nydus are spotted (and in that case immortals are better against queens).
In lategame, they have a role against corruptors, since VR are armored killers. With 250 HP, 4 supplies, and the highest anti-armored DPS of the game, they’re not scouting units !
Anyway, their design comes from their role. It’s as if I said : well reapers aren’t popular in lategame. Let’s give them +120HP and +2 range so they can be used as scouting units AND heavy assault infantry. That’d just be broken ; it’s not their role.