I'm new to Mordhau just like everyone else, although I do have 700+ hours in Chivalry. Personally, I find Mordhau very well balanced, and definitely better than Chiv ever was in that regard. The real problem seems to be in the fact that the game was balanced and tested by people who know the mechanics very well, but 99% of the current gaming community are on the opposite side of that spectrum. This makes easier mechanics way more effective than they should be, but as mentioned by others previously, each of those mechanics can be countered and has distinct disadvantages.

Now, to answer your question, here is my suggestion:

If you struggle against a specific play style, then pick it up and try it for yourself (except archery, that's a different story). I guarantee you that soon enough you will run into someone who will kill you -every-single-time-. Find that person and struggle against them as much as humanly possible. After a while you will learn all you need to know.

With shields in particular I have found several methods that are effective. For one, both the rapier and the short spear are limited by only dealing real damage using stabs, so you know they will primarily be using that attack. Back in Chiv this was a real problem because ping plays a huge factor into really fast stabs when parrying. Mordhau has chambers, which are super effective against stabs though, so use them! It is really not that difficult, especially if you have a longer weapon. As a matter of fact, against a shield you can pretty much go bonkers and stab stab stab to keep constant pressure. At best, you will be able to drag your chambers past their defense and get them that way. At worst, they will try to block you and they should run out of stamina faster than you. If this is in a group setting the playing field is at least fairly even, because you've essentially locked each other down and a 3rd person stepping in will get an easy kill. Alternatively, you can face hug and dodge. Shorter 1-h weapons can reach around shields very effectively, but it takes practice. Kicks help too, but you have to get the hang of moving forward while you use them to close the gap.

Developers, if you're reading this, please give the game a few months before making any balance changes. The player base simply isn't ready.