Your argument is... odd.
You want to "Add a speed boost" "Because cobalt is a really great armor". So you want to make something that is "really great armor" even better...
You don't say why the armor is great; you just say that it is great.
You say that it has great visual design, but that's after an "and", which means it is is a separate argument. So why is Cobalt great in your opinion aside from the visuals?

You've told me what you want to do, but have not given sufficient reason to persuade me that it's a good idea. Just because something doesn't have as good stats as other things doesn't mean you should arbitrarily give a buff that you want to have.

MSI in particular doesn't fit because it's a special ability for special armors, which is in part due to the fact that SK is meant to be played with the team moving together, not with teammates running ahead/falling behind (as far as I remember someone saying that this is the reason why MSI has been so limited). So having standard knights run faster than the majority of the others isn't quite right.
ASI might be an okay buff to add, seems fairly straightforward, but for me the image of a standard knight isn't one that attacks faster with all weapons. Certainly a skilled knight would be able to attack faster than a standard knight, but I feel CTR or DB would fit better for an image of a standard knight. And of CTR and DB, CTR is the more interesting of the two as it's currently limited to bombers and Chaos-glass cannon Knights.

If Cobalt were to get a buff, CTR low would be a pretty good choice. It'll give more options for hybrid gameplay(utilizing Levi, Nitro, Vali) while keeping in mind that the recipes are free from the missions(so, not giving a +2 buff at 5*). Universal DB would help with hybrid, but CTR helps bombs significantly more than DB. I feel CTR would help the three weapons much more equally than DB would (because bombs are underutilized, so it should lean a little towards bombs).

Thagx makes a really good point, you shouldn't get a great armor for free, you should have to work hard and go the extra mile before you start getting buffs and bonuses.

I still think personally that the armor doesn't actually need a physical buff and just instead needs some sort of price decrease. It used to be leftover things from early development if I recall and is something that's on the bucket list.

The armor is from my understanding the "Cheap" Armor of this game: It has decent stats but is overall one of the worst pieces of gear in an RPG, but can get you through a sticky situation and help you get better gear.

P.S.S. cobalth branching out to multiple armor paths

Spreading Casu marzu on Pane carasau doesn't make the former any less putrescent.

@hex Cobalt is not putrescent. It trades away special resists for large health pip amounts.

Azure Guardian does not give any more of a health bonus than any other armor. The only advantage it has is the 10% increase in normal defense, but we already have Ironmight for a normal-orientated pierce defense armor (Jelly Mail is the pierce-orientated pierce defense armor)

Vitasuit Deluxe is in a bad spot because not only does it have no 5 star version, it also is directly inferior both health boost-wise and defense-wise to Ancient Plate Mail (an armor that is already not very viable for most levels)

Almirian Crusader is... not even semi-decent. It's in the same spot as Azure Guardian, the 10% normal defense increase over offensive armors like Snarbolax and Deadshot is its only redeeming factor. The only reason it's not completely obsolete is that we don't have a shadow plate mail. (so it has the highest normal defense of any shadow armor) Trading off a common status resist in order to obtain status resist for a rare status is not helping its cause either. It's supposed to be a restored armor, yes? Why does it retain the undead-matching weakness? (but none of its strengths... We already have an undead armor, Almirian Crusader is acting as if it's the castoffs from Skelly Suit. The equivalant situation would be if the gremlin helm, Seerus Mask, was split into a helm that protected against shock and fire, and a helm that was weak to frost and freeze. Total pointlessness.)

So the issue does not just lie with Azure Guardian, but every single sidegrade of the cobalt armor line. Aegis could do with a reworking too. Not Heater Shield though, it's fantastic.

it's kinda underpowered if you compare it to others like Chaos set

Everything's "kinda underpowered" when you compare it to Chaos set.
Ignore chaos set, compare it to other armor that should be "middle ground". It's a defensive armor, and it's not even as good as the other defensive armors.

Missions are centered around obtaining Cobalt gear - it's too easy to get Azure Guardian. The missions give you enough orbs to craft and the recipes, and all you're left to do is farm remaining crystals.

I don't mind people saying that Azure Guardian is fine the way it is since it's cheap.

What does bother me is that both the armor's sidegrades are rubbish too.