I kind of get what you’re saying but at the same time. I don’t. Having a 5 frame normal is an advantage if you have a situation where you can place yourself at +2 on block, or whatever, as whatever they press will get stuffed, but the same is true for most buttons the opponent presses at that point in time.
So if you’re character doesn’t have a 5 frame medium, they can use a 3 frame jab, if it counter hits, they can get a counter hit combo into medium, for very similar, if not more damage to those using the 5 frame medium.
You also neglect an option that people have in this situation, which is the reversal. You say in the second paragraph that the only option is grab or block, but they can also throw out a reversal which will beat both the medium attack or throw options. Obviously this is high risk, but sometimes you have to make a read. You describe the 5 frame medium as an option select that answers everything, but it stops being as threatening if your opponent is aware of your reversal option. If he’s smart, he will try and bait this out, making the situation a sort of rock paper scissors scenario (I say sort of because it’s actually much more complicated), where your block beats their medium but loses to their throw, your normals lose to their throw or normals, but give you frame advantage on opponent block, your reversal beats their medium or throw, but loses to their block, your throw beats their block, but loses to their normals, and your neutral jump loses to everything but gives you a punish on command throws, and usually frame advantage on regular throws.
Ultimately, if you’re at frame disadvantage in SFV you’re now in a much trickier situation than you were in IV, but I don’t think (due to things like counterhit combos) it makes a huge difference if you have a medium with specifically 5 frame startup. Even without that, there would be work arounds… for instance Rashid’s standing LP is +3 on block, so even if his mediums had 6 frames of startup (they have 5) he would still have a frametrap that beats anything but reversal with invulnerability frames.
I think your problem more regards how the game works, how frametraps work… and you’re right, it’s a much trickier situation to be in in V than it was in IV, but in IV, crouch teching arguably made this situation pretty mindless, placing even more emphasis on execution, and away from strategy. It’s been clear from the outset that Capcom have been trying to change that with V.
I guess a TL:DR version of my post would be that ultimately Capcom don’t expect you to have 5 frame reaction time, they expect the player with momentum to be at an advantage. You DO have options in the situation you describe, but they are not as favourable as the player with frame advantage. If this however is a problem with your game, then you need to be thinking about what is putting you in these situations to begin with. If you’re letting your opponent jump at you, for instance, you are giving these +2 situations to them for free, and of course, you are going to have a very hard time as a result.