The Blue Shell is a necessary balancing element, simple as that. It's undeniable that once a player gets in 1st they tend to stay there, the Coin system and the fact that 2nd place rarely gets Red Shells only ensures that. I would consider myself a pretty good MK player all around, not top tier by any means, but very consistently good. When you're online and playing against people of similar skill level, when you get in the back of the pack it's almost impossible to get out of it because people get and will use the top items indiscriminately to try and get into a higher spot. Once 1st finds a breakaway early in the race, ie. 2nd and 3rd taking the brunt of the incoming Red Shells or other items from 4th-7th, that normally gives them enough space to just cruise until the end.
I hate when people say "Blue Shells are n00b items" because they're not. So much of the game relies on luck, and in a perfect world for Blue Shell to not be required in the game would have to have everyone to be of the mindset to only attack people in 1st place, unless they have an extra Red Shell and 2nd isn't holding a blocking item. You simply cannot beat someone in MK on speed/skill alone once someone gets ahead (when people are of a similar skill level anyway, but even mediocre/moderately good players will beat top tier players if they get a decent distance ahead).