There are a couple of ways to look at this. If a gymnast falls all over the place at state and doesn't qualify to regionals, then obviously you should look more at the season as a whole and at acquired skills. However, if the gymnast hits to her best ability and still doesn't make regionals, then will the same gymnast be competitive at the next level (especially one that tends to have a lot of repeaters)? Some girls can really upgrade and improve over the summer, but even though I had a successful L8 season, I was just buried beneath the 4th-5th year level 9s. Of course, that may not be a concern for many gymnasts, especially if they're older-- I convinced my coaches to move me to L9 my senior year. Even though I didn't make Easterns, I made it to regionals, actually placed 3 events and AA at state, got my L10 mobility score (although that goes hand-in-hand with making regionals), and, most importantly for me, was able to say that I was a level 9.
Next year, though, there will be a significant difference in the skill level between L8 and L9, so you may very well see a lot of gymnasts moving up who don't quite have competitive L9 routines. On the other hand, you might see a lot of really, really good L8s who wouldn't be competitive at L9. It will be interesting to see which way gyms choose to go with their "L8.5s".