first in naxxramas meta i build a taunt druid that had a 60% winrate vs undertaker hunter but a 40% against everything else. I made it to legend in 15 days ( and that is back when you needed to grind from 0 with no star bonus or floors).
Now i can get to day 1 legend with any deck. this month it was anyfing paladin,last month agro murloc, the month before DMH (could not play day 1-2 so it was day 3)
Standard (playing since April 2020): First was Spell Druid (May 2020), this month it was primarily Zoolock Wild: (playing since 4 months): First was Big Priest 3 months ago, this month it was some Reno Quest Mage and some Darkglare Warlock
I never bothered with more than rank 5 in the past. Just came back from over a yearlong break and decided to make the climb for the extra rewards.
Secret mage was really easy to make it with. The only consistently hard match was other secret mages, but most of them were idiots and would play counterspell when I had coin almost every single time. Insane that a 2280 dust deck climbed to legend with a 60-70% winrate.
First time I got legend was with control warlock back when the cubelock meta was on. I played my control lock with double sacpact, silence (for the cubes) and rin first deciplin . It absolutely destroyed the meta.
Recently I hit legend in January with big warrior. That deck was a aggro killer