#2 Putting Legends/non wrestlers over current talent
Edge speared Elias at SummerSlam this year while Goldberg received his redemption after putting away Dolph Ziggler at the same PPV. Those are just two recent instances of creative always using current stars to put over WWE Legends.
If it's only done once in awhile or a couple times a year, then it's fine, but every time some big name from the past shows up at RAW, SmackDown, or at a PPV, they are likely going to hit their classics at the expense of a full-time star.
It is true that nostalgia is sometimes needed, but if some of the newer stars are going to get over, they need to triumph over the WWE Legends every now and then. Stars working with Legends do get somewhat of a rub, like Becky Lynch did recently with The Rock. King Corbin, however, wasn't so lucky.
There have been some instances of this working out, as Ronda Rousey was a full-time performer for her first year. She picked things up quickly and was a legitimate star. Even Trish Stratus, arguably the best women's wrestler in WWE history, put over Charlotte Flair, but in that case, Flair didn't need putting over, as she had already won major titles on numerous occasions.
The main point is that it's okay to have WWE Legends go over Heath Slater or stars lower in the pecking order, but if the company is already having trouble getting younger stars over, then have a few of them go over a star from the past. It would do wonders for a young up and comer's career.