I think they answer is yes, they were justified. Which in some ways makes this season even more disappointing. Yes, the Astros finished at 86-76, but they also finished with a +111 run differential. They scored the fifth most runs in the American League, and allowed the fewest. We can come up with explanations for why this is, but I think it's safe to say that if they repeated those numbers in 2016, they'd be far better than 86-76, and would finish much closer to their Pythagorean record of 93-69. (I didn't just make my prediction up).
And, Correa was going to get a full season of at bats. Gomez too (who, despite what you may remember, finished the season hitting .318/.370/.571 in his last 19 games last year). The rotation that had the second lowest ERA in the AL, with the third lowest FIP and xFIP, was going to replace 24 starts from Scott Kazmir and Roberto Hernandez with Doug Fister. No loss there, and a potential gain. The bullpen, which, September struggles aside, ended the year easily among the top 5 in the AL, added the fireballer every one said they needed. There was very little reason to expect them to get much worse than their +111 run differential, and a lot of reason to hope they'd get better.
Instead, the bottom fell out in nearly every way it could. The fireball reliever became a HR machine. The reigning Cy Young award winner is sporting a 5+ ERA. The pitching staff that allowed the fewest runs in 2015 has allowed the most in the AL in 2016. The hitting has also dropped to 8th in the league, with some of the worst RISP at bats you can see.
If the Astros were sitting with a +20 run differential, and were below .500 or worse, then we could start talking about whether the lineup construction or plate approach is producing a team that consistently under performs their RS/RA. And how, because of that, maybe we should have kept our expectations in check.
But that's not what happened. The 2015 team was not a fluke, and they were not lucky. They were a good team, that, if anything, under performed. The -36 run differential so far is shocking because it came out of the blue.
The good news is that this is mostly the same team that had a +74 run differential from May 3 on. If they manage to repeat that, history says they will be much better than 68-69. Whether they will or not is another question entirely.