We just got done saying tippers are naturally inconsistent because of you can't control who your opponent is, where they are, and what animation they're in. The effects of all that being exaggerated by the sourspots out-prioritizing the tippers at points of overlap. I cannot use Marth against Charizard, DK, Yoshi, and a few others solely because their weird character model makes tippers super difficult (my spacing at this point is top level).
What you want is early Smash 4 (though you're asking for even worse tippers than that). To compensate for that, sourspots would have to be strong or damaging, or Lucina would have to be heavily nerfed in damage. Where have we seen that? Smash 4 release Lucina. That damage and kill power was totally unfair for her, but it would have to be the case if Marth's tippers were "much hard to land". And then Marcina can go back to being bottom tier. See how it's a balance?
Or if we just say **** it, who cares, make tippers difficult even for top players and keep Lucina the same. Well, then we just got rid of a popular and iconic character in Smash, didn't we? A unique character that teaches its players how to do something that's important for any character in competitive play: Spacing. A character whose damage properties make too much sense – weakness in the arms (with small hitboxes that miss up close all the time), so-so reward in the middle, and full strength at the end where the blade is physically moving at its fastest angular velocity.
It's even worse on the casual side. One of Sakurai's main goals since after Melee has been to make the game easier for players, especially beginners. The beginners already have much more incentive to play Lucina as it is. He wouldn't completely remove Marth from their consideration by effectively making him unplayable for them.
I get where you're coming from. I criticized the tipper hitboxes moving outward on a few of Marcina's moves in that one buff. "Easier tippers is not what we need", I said. "Reduction of lag is what we needed." But then I realized after several months, they knew what they were doing.