This depends heavily on region, Regions like Oceania and asia i would say it's a hell of a lot easier to get to higher ranks purely because the competition isn't as fierce.
i feel like radiant is always the same in every region but if u put a team of NA/Emea immortals on a team vs Asia/Oceania Immortals the NA/Emea team would win 7 out of 10 games comparatively, but it also comes down to factors like does the NA/Emea team work well together, Does the Asia/Oceania team work well.
If your talking solely NA/Emea i feel immortal is the high elo, I've spent a lot of time and I'm only consistently d3/ascendant and I don't aim train, max 3 dms a day and get carried by util usage and my gamesense, i have 1 of the 3 pillars and am still consistently ascendant.
I feel like in Oceania or Asia i could reach ranks like immortal 1/2 with my current skill set just based off stuff i've seen myself.
that's my perspective :D