With the exception of MK8D, Blooper is super useless as an item. It was somewhat effective in Mario Kart 8 since it did a better job of covering the screen and also made your traction a lot more slippery.
But then it was downgraded even more in Mario Kart Tour because not only does it no longer make your kart slippery, but it's even easier to get rid of the ink. Any kind of boost, including trick jumps or mini-turbo boosts, will get rid of the ink. So it's more useless than ever before...
There's something else you didn't mention. Even Mario Kart 8 and Mario Kart 8 Deluxe, where it covers up more of the screen, the Blooper has a lot going against it. A lot of tracks, especially in the newer Mario Karts, have a lot of boosters scattered around on jumps or just hanging around, and by just hitting one of them, that ink is just gone. Maps that have boosters everywhere like Wii Rainbow Road? Forget about it. Even on water maps like N64 Koopa Troopa Beach or Dolphin Shoals, there is now way that ink is staying on your screen for more than like a second.
The bigger problem to me is that there is an unproportional gap between how good it is against skilled players versus how good it is against new players. Picture this: if you're playing Mario Kart with your aunt and she doesn't know where she's going to begin with, she's pretty much done for when the ink hits the screen because she can barely stay on the road in the first place, but then if you're playing with more skilled players that already know the map, you know, the people need to hinder the most with your items, that ink isn't going to do jack squat because the best Mario Kart players have the layouts of these maps permanently engraved into the back of their skulls. It just seems so anti-Mario Kart in design because you look at items like the Bullet Bill or Lightning, and those are items very clearly made to give less skilled players a fighting chance. Meanwhile, the Blooper completely spits on that design philosophy.
I agree with you that the Blooper shouldn't even be an item to begin with anyway. Also, the Mega Mushroom. POW Block, and Thunder Cloud from Wii never should have been added to Mario Kart in the first place (especially the POW Block and Thunder Cloud, like seriously, who thought designing an item that actively harms you would be a good idea?), and I hope they never bring those items back.