Question

Hello Everyone! You might know me for a post I made some time ago introducing myself. Now almost a month later, I am rank 4-2 and I am loving this game to bits. When I got to the hall of heroes, I got interested in Izola's (Guardian) gear, since I love playing as tanks, but is it a good thing to do? Is the armor good?
Regards

I have a detailed armor guide that you might find useful. It explains basic principles and gives you options for each play style.
In short: No, Izola's armors are not very good, as Neueragon said.

I don't think being a tank is ever a good idea. Evading is the way to beat the biggest foes. Everyone just evades and shields.
Oh and do you see the defense for the Plate Armor being in the normal category? Some monsters do Purely Non-Normal damage with ranged attacks.
Everyone in PvE evades.
Everyone in PvP evades. You get the point.

But is the guardian armor really bad or just underpowered?

But is the guardian armor really bad or just underpowered?
It depends on what you mean by "bad". Is it so bad that you can't play the game with it? No. You can play this game with just about any armor. But is it so bad that it is clearly outclassed by other armors? Yes. So there is almost no practical reason to choose it.
It's all because of how damage calculations in this game are tuned. A highly defensive armor protects you only slightly more than a weakly defensive armor. So most players end up choosing weaker defense that comes with offensive bonuses. You can't tank, so you have to learn how to dodge, as all of the players in this thread have said.

Well then that's stupid, why make an armor that was made to be used as guardians that need to use their charge attacks to do significant damage if it doesnt protect you at all? I mean yeah I can evade, but while im attacking, the animation is so long that monster can easly attack me

Yes, the armor in this game is not well balanced. For example, almost the entire "Other" category in my armor guide is useless. Here is a big thread from this month, in which players discuss how to rebalance armor.
As the end of my armor guide advises, don't spend much of your time thinking about armor. Spend your time thinking about weapons and play styles. That's what's interesting about this game. Happy travels.
as a rule of thumb, good armor has either offensive boosts (wolver line, padded line, chaos and so on) or good defensive capabilities such as multiple useful status resists (grey owlite, ice queen).
beyond that, you also have gear that is very useful in certain situations, but terrible in most others (deadshot, virulisk, dragon scale). then there are also some bad sets that make little sense (salamander, it has ele defense but buffs slime damage), while others are terrible because they lack any kind of boost (cobalt).
the plate line is close to the last category and would be in it if it didnt have stun resistance. stun isnt very good though.
to sum it up, no, dont get it. plate isnt even tanky, as defense doesnt do too much and it lacks non-normal defense. if you want tanky, become a vanguard and farm FSC to get enough tokens for ancient plate, which is similar, but has a significant health boost.
if you do want to go somewhat tanky, pick something like grey owlite. if you want to have something good, pick something that buffs whatever weapons you prefer.