No other live, primetime scripted, American television program exists let alone produces as many "new" programs without repeats per year as WWE so naturally repetition will exist. Shows eventually decline in quality and ratings and go off the air (The Simpsons, ER, Law And Order, etc keep going but don'' create as many shows per year as WWE) but WWE keeps on going so naturally things are going to be as they are. Also the way that fans view the product these days with many actively searching for flaws, rather than just knowing that they exist and still enjoying the good parts, of course things will be viewed as declining. These days fans are conditioned to expect things to happen very quickly and a lot of them think that their way of doing things is the only correct way. With that mindframe being common amongst the majority, naturally the decline exists.
TNA is improving, but to compare the current situation to that of 1996 isn't fully accurate considering many factors. At that point in time WCW was competition. Currently TNA is morsoe an alternative than competition. Sure it's a competitor, but overall, the situation of people choosing one over the other isn't much of a factor with the shows airing on different nights. Sure a lot of people will only watch TNA and not WWE, but not enough people have that attitude, to t affect things in the same way that the WCW situation did. (OF course a lot of people watched both companies back then as well). If it was full fledged competition, then things might be more similar.