In having been bored during lockdown I decided to open up more of the game on my son's profile (the secondary profile) so that when playing 2 player, there can be more options of costumes for the second player rather than the defaults (quite why it's done like this and they don't get player 1's choices I think is ridiculous, but I digress).
Granted it helps that I have the Kombat Pack and the DLC code version of Kold War Skarlet, therefore some of the great skins for the likes of the classic male ninjas, MK3 Kung Lao and Sonya (the Kano one is hideous and the story mode updated version is WAY better), movie Shang, workout Cassie, the aforementioned Skarlet etc. are tied to my whole console rather specific profiles so they're already in the game, but I have noticed that I've unlocked some of the skins and gear pieces I spent months pursuing during my main profile play through within just the last few days.
I'm trying my best to recreate as many characters to how I have them on the main profile, or at least close-enough so they generally look to be the same-enough choice when chosen as player 2; as such i'm not going to go out of my way just for a preferred Sindel kwan dao or Rayden amulet, as long as they're 95% the same in really noticeable accessories and their skin then it suffices for two player mode. I'm sure I must have spent absolute weeks working through with Jade to eventually get at least a human skin, then the red and green hooded skin, then a drab olive green skin (but at least it was green!), before eventually unlocking her most classic one Honoured Tradition after god knows how long (and at the time I didn't realise I could get the hooded one in her proper colour from the tutorial... or could skip directly to the character tutorials haha). Got it this time around with her classic mask within a couple of days!
It definitely seems like the more desirable stuff has become more reliably obtainable in the months of patches and updates since I first began playing a year ago on the main profile.
Not excusing any of their content-unlocking design choices, but I'd never bothered stocking up the second profile because I quite literally felt "I am NOT doing all that again" yet to get some of my favourites, it's been a lot easier the second time around than expected.