The top level is so disconnected from lower leagues they just spew false information constantly. It's the equivalent of asking Bill Gates for grocery store prices.
Outside of the very, very, very low end of F/Bronze 3 the people do know how to play, and will often even use actual builds. The main thing is that the execution is horrible, builds are often suboptimal or only go to the second supply structure/ovie, and the players fail to or improperly react to their opponent.
You'll hear people say that all you need to do is max out on X unit and then a move to win, but that's not really helpful advice unless you have the macro of a GM/S rank player. It's not necessarily wrong to just focus solely on your macro until you get that, but being a complete player is important as well.
The biggest things that helps people rank up from my experience is remembering that the other guy is panicking and guessing just as much as you are, and that having a focused practice target and actually playing games you won't get better.
There was recently a video actually of Harstem and Artosis trying to guess the rank of a replay, and there was one where it was like Silver 2 or something and one of them guessed Bronze 3 because they couldn't think anything is worse. They're just disconnected completely and spew nonsense about it.
One of the best suggestions I can actually give you if you want to listen to a high level player give advice is to check out WinterStarcraft. He's too edgy to be as popular as the other SC content creators, but he does a series called Angry Coach on twitch/uploaded to youtube where he coaches players of all ranks (he's personally high masters currently I think but has been GM in the past as random). Aside from being extremely good at guessing people's ranks because of this series, he knows the common rank plateaus for the different races and why they occur, and gives decent advice on how to improve your play.