They had to play against the 1st, 2nd, 3rd and 7th ranked teams in the world in order to qualify - I wouldn't read too much into them not making top 8 when some of those that *did* make it had much easier routes. This is the best NiP have looked since early 2015, and even though they didn't reach 8th place in a big tournament I'd still argue that they are a top 8 team in the world.
I don't think that this NiP lineup will become the best through hard work and friendship, and I agree with you that it would be a naive viewpoint for one to hold. I simply don't believe that we've seen the best from them yet as their lineup is still relatively new, and regardless of whether or not that actually turns out to be true - the team seem happy with the progress they're making and committed to improving from the comments they've made in interviews, on twitter etc., and I doubt that will all be torn asunder simply because flusha is announcing his free agency.
It's hard not to ignore that this is flusha's lowest rated major, and big event, ever. Do you honestly think it'd even be worth it to take a gamble on him when he's so out of form?