#4 Too much emphasis on part-time talent
WWE's insistence on featuring part-time talent in a handful of matches each year at the expense of up and coming talent has damaged the product. Having big name stars come back for one big match can sometimes be a good thing, but often when they hold titles and take spots from current stars it can be a problem.
Take Undertaker returning and defeating Rusev in under 10 minutes as an example of this. Taker beating Rusev and then going on hiatus again does nothing for either man and it is short-term booking from WWE.
A better idea would be for them to have a two or three match programme, whereby Rusev could go over in one of their encounters. Taker just showing up, beating Rusev and then leaving again hurts the Bulgarian and gives the Deadman an unnecessary victory.
Another example of this booking is Brock Lesnar holding the WWE Universal championship despite not being in a full-time role. This is a problem because the top belt on Raw is part-time just as the champion is, and so it loses its prominence. When a part-time champion comes up against Roman Reigns at WrestleMania, it is not a massive shock that a lot of the fans don't care about the outcome of the match.
Also, the fact that the only Superstar Lesnar has been pinned by in recent memory is Goldberg (another part-time star). This says a lot about how WWE values its current stars. It would have helped Reigns if he went over Lesnar at WrestleMania, but for some reason, WWE held fire on that one.