Mario Maker can be a lot of fun, though you gotta develop skills at telling which levels will be good and which will be shit pretty quickly. But if you do then you can find levels with some incredible creativity and fun unique challenges. There are also some good resourses online for finding great levels.
Yeah I was playing the Mario All Stars version of 3. Beating every level was definitely possible that way only restarting at the start of every world, but it was still a significant challenge since some of those later worlds are so long and have some really tricky levels. World 7 was definitely the most challenging, though I recall 5 and 6 having from frustrating levels too.
It's funny, because the worlds in 3 were so long it actually was more difficult for me than The Lost Levels. Even though The Lost Levels were insanely tough the fact that you only ever had 4 levels to get though in each world meant the setback wasn't as tough to overcome if you got a game over.
I never bothered doing the full completion in my early days playing it though, I would just do the trick of getting the flutes and warping. To be fair there was never really an incentive to do so beyond your own satisfaction since there were no collectibles and the game didn't track your completion % like World did. I have no idea how anyone found out about the white block squat in the first place. It must have been one of the programmers leaking the secret or something. I don't even know where I learned that trick from, it just seemed like something I've known ever since I started playing the game.