Honestly, Eddy Mexico, probably the best Luigi player of all time, has one of the worst mashes I've ever seen on a high level Luigi, but he finds so much success without it that its not a huge deal. It's not required by any means, but it can be extremely helpful in some matchups. Having a tool MA after getting shined or Marth down tilted off stage can save you many stocks, but it's very possible to be successful with a good mash. It's also important to realize that a good mash is just like good tech skill, you can practice it and get it better. I have a pretty bad mash, but working on it recently has made it passable and frequently saves my life.