Can every card be Amazing? how can you have an amazing card if you don't have poor cards to put next to it?
Also - look at the pre-release frenzy before every wave - Arvel was hailed as brilliant and amazing before people actually started using him.
There will always be multiple tier cards - and the position of those cards can change place - Imagine in a future meta that there is such a flood of stress stuff released - that PTL becomes a very bad choice to take. Cards have counters, and even the terrible cards have use somewhere - and as the game goes on, their niche may become more distinct. Already - if we compare an A-wing Pre and Post Rebel Aces - we can have a Green squad with PTL for 22 points - Vs, Green squad with PTL, Expose and refit, for 24 points, it's as if we now have a 2 point version of expose, from a certain point of view. (Let's not get into the argument of what you could take over that 4 points of expose...)
Part of the game is in valuing cards, part of the game is also in the casual world - where Arvel is awesome if you want to run him as green leader when you do a battle of Endor. Not every card needs to be great.
Let me be clear - I am not saying that FFG should run out and design terrible cards - just that it's inevitable that all cards can't be equally awesome.