2100+ are a quite impressive rating for sealed mainly, where some luck factory may be involved also Justice's 41-4.

I would like a deep answer how to get better/improve Sealed game if some top player don't mind write alot, now I just can't reach 2K+ rating or beat a good player with bad card set ( that's I guess it's the secret, how to play worst cards, if there is worst cards or just worst strategy), feeling "stuck" .

I also would like to leave a question:

Would it possible to always win by skill ? Like in chess or pro korean SC players ?

Of course, by what else would one win? There's only little luck involved in my opinion (more the coin tosses than what card you get).
How to get better: Practice, practice and more practice And watching replays is also a nice way to learn new moves.

Possible but highly improbable
Since its sealed at some point you bound to get the worst possible deck on worst possible map against the worst possible deck opponent has and worst possible luck
With godly skill you could get about 10-20:1 ratio of winning but to win 100% of all times is highly improbable

This game fundamentally different from chest and SC since in chest you and opponent get same units while in SC you and opponent could pick your race and all race relatively even
But on sealed you cant exactly pick your card thus improbable to win 100% against good opponent with otherworldly card when on the other hand your cards is crap and also theres additional luck factor too like coin toss
However it's more highly possible to win 100% on constructed assuming you can use all card you want and your skill is godly

the biggest difference between sealed and constructed in my (humble) opinion is that sealed forces you to adapt tactics to your cards selection available.

if you always like to do the AA recon art approach, and your selaed deck does not support this at all, then you should see what type of deck it will support instead, every unit has its uses and its weaknesses, and almost every sealed selection can make one sort of combination.

combinations i like to find are

helies and AA and some air debuffs
planes and tanks/ art with some ground debuffs
the art and recon combi
transports and we need reinf/ high octane

try different tactics with constructed decks and you will see more options with sealed selections.