What sets apart End-game Players from Mid-game players?

Before diving into this question, I want to put it out there that I'm not looking for meta builds or anything like that. I am very happy with my progress over the course of these past couple of months trying to buff myself up with mods, weapons, frames, and I've probably sunk more time into this game over the past week that I ever had over the entirety of my 400+ hours.

With that out of the way I got a question more specifically towards those who comfortably play the end game content, or can reliably succeed those kinds of missions. But I would still love to hear what others have to chime in.

(Will summarize at the end!)

I am currently MR22, I don't know if that's particularly high but given my playstyle, I kinda feel like my rank doesn't fit the "expectations" that come with being that high, for years(I had an older account reach 11), my time on Warframe consisted of grabbing every weapon on one mastery rank and completely lvl them up and then move on to the next rank, and with the old peace update on its way I felt it was about time to try and really grind my way into that "End-game ready" state. So I farmed primes, traded, even just finished all the quests. But now comes my problem, as I was playing, I noticed that I can succeed with 30-40 lvl enemies comfortably, even if it took more than one shot, 50-60 would require me to spam my CC abilities (proud Frost Main❄️🧊) but I was able to complete those, however as I got to 1999 and the lab, I was clearly lagging behind other players and was essentially getting carried to victory on missions.

As someone who likes being able to decide whether or not I wanted to search through every corner of the map or blitz through it, I realized that I didn't have the proper strength to do that. And when I look through the subreddit or YouTube for advice or tips, I've seen some people post how they absolutely shred through lvl 100+ enemies or their knowledge on "hidden modifiers" for certain weapons always impresses me but I found it hard to grasp because I didn't have my own point of reference to piggy back off of. So if you are someone who frequently plays modes like steel path, or have maxed out or ran through anything considered "End-game" confidently, I would love to hear your opinions on where you believe that point is where all of Warframe is just open to you. And if there is anything you believe that separates end game players from others, what would be the deciding factors.

TL;DR - I feel too weak for my MR and not doing as well as I would like in higher lvl missions. Do you believe there is a bottleneck between End-game and Mid-game content? what would you consider to be the transition point?