Not being able to block while kicking (or reducing it) wouldn't stop you from being able to kick players aggressively coming towards you. All of those kicks Menethil did in the videos above would still be possible; I don't think he blocked an attack while in the middle of a kick. So, you'd still be able to kick someone if they're coming close to you. It's just you wouldn't be able to stand on one leg while kicking and blocking attacks at the same time like a juggler.
Look at how annoying it is to fight someone who's kicking and blocking all the time:
The two times I got kicked, I came in too close and left myself vulnerable to it (although he still had to block while he was kicking for it to land). Other times I was keeping my distance while attacking, just because of how much he was kicking, yet it was really frustrating how he was able to block at the same time, as if it didn't matter he was kicking. And at least there it was an isolated 1v1 fight on a public server. If it was in a match, there's a lot of pressure to kill an archer quickly before enemy cavalry comes to help, so it can be all the more annoying. If you try and outrange them, they just leap away and fire off another shot. If you circle around them, they can still stun you by kicking towards the side in anticipation, and still block because they'd be faced in the right direction. Sometimes it's possible to go round to their back while they're kicking and land a hit, but it's not always reliable, since they often magically snap around and block the attack somehow. You can jump over their kick, but that's a gamble, they can still block (without a shield, unless their ping is high), and if they haven't kicked they'll probably leap in the other direction and fire off another shot, constantly kiting. Archers are meant to have lower proficiency in melee as a trade-off for not being infantry, yet the ability to spam kicks while blocking can make it moot. I'm pretty sure duelists have complained about "Turkish kicks" in duel tournaments too. It's not fun to fight against.
I tested it in Bannerlord's Custom Battle, and it seems like it's just as easy to block manually while at any point of kicking.
Remove the general block delay and apply it to kicks instead.