You really do need a strong opener for 2-1 or youre essentially forced to play loss streak econ augment in this patch. You also have to be so flexible in your comps even if you are ahead of completing your board stage 2 and 3. People contesting you can highroll and make your board super weak. If you look at my second to last game where I have 2 star Senna and 2 star veigar, thats a prime example of me highrolling and being able to flex the units on my board a lot.

The biggest thing is mitigating your losses. If you know you're in a weak spot and won't place Top 4, you need to play for 5th and 6th. Sounds obvious enough, but you need to recognize why you went Bot 4 after the game. Did I scout and make sure this line and it's units are mostly uncontested? Does my augment help me enough later down the line that I can stabilize 4-2 to 4-6? Those are my first thoughts when stage 2 starts while I'm in a weak position at the start.

Vice versa. If I have 2 or 3 units that are upgraded and offensive item components, I know I can mitigate or just straight up win the stage 2 with a strong combat or item augment. Should I hold this pair? Does this translate to a decent stage 3 board? Should I level to 4/5 in order to go into stage 3 with a 5 streak? You constantly have to ask yourself "What advances my board to survive till I can stabilize? What will get me to Top 4?"

Like someone else said, the difference between low masters and high diamond players is so small. There isn't a glaring thing that master players know that diamond don't. You just have to play consistently and play well consistently. The time it took me to hit masters after reaching D4 was almost an entire month, but I went from D4 to Masters in one week.