I haven't had a whole lot of time with MK11 yet, but I've finished all the main tutorials, tower tutorials, and a couple character specific tutorials, as well as finished up through Chapter 4 of the main story.
It definitely seems like unlocking everything would take an enormous amount of time, but I don't know that I would call it "grindy", as it doesn't seem like something you'd really "grind" for. The rewards you get in the Krypt seem to be random, but I could be wrong.
The amount of Kosmetic items in the game is absolutely insane. Each character has close to 100 unique, unlockable character details, split between costumes, weapons, masks, etcetera. Scorpion, for example, has a category of spear heads.
In addition to these costume pieces, there are also unlockable fatalities and brutalities for each character, as well as between-round taunts, the animation that plays at the beginning of a match, and the victory pose.
There's also a ton of koncept art for each character (roughly 8 per character), and you can unlock maybe 20 music tracks, and another 50 to 100 main story concept art pieces.
And that's not all. Each player has their unique "Kombat Kard", which shows your level, icon, background picture, etcetera. There seems to be hundreds of kustomizable art assets that you can unlock to show off your achievements.
I'm probably forgetting something, as there are truly a mega crap ton of unlockables.
I haven't played enough yet to notice any sort of "scam", or incentive to spend money.