I think it's very possible that the M's overachieved last year and revert back to being an under .500 team. Overachieved is probably the wrong word, but they are typically so bad that I will use it. I'm still scarred by the 2010 season when they acquired Cliff Lee after a winning record in 2009.
I'm not sure where you're expecting the regression. Who had years last year that would make you say "wow, they really out performed their normal ability level?"
We are talking about the Mariners. Questions at shortstop, first base, and the outfield. Cano's power decline is at least a little concerning.
Felix reverts back to a 3.00 ERA instead of 2.30. Iwakuma was terrible in September. Walker and Paxton are still unproven and Paxton has been injury prone. Chris Young was pretty valuable last season. The bullpen was outstanding last year. They likely take a step back.
They might be better, but there are still tons of question marks. I get why they will be better. Oakland rebuilding helps too. We will see what happens.
Not even really sure if I care about Cano's power. Only 11 guys in the majors hit 30+ homers last year. More interested in him continuing to be a .300+ hitter, working counts, and making those around him better. More concerned about him at some point losing some range at 2nd base.
I get what you are saying at the position where you are worried. But I have reasons to believe that we'll be better there. Performance of the Mariners lineup by position last year:
C: .206/.254/.378
1B: .252/.314/.399
2B: .315/.379/.448
3B: .264/.329/.447
SS: .242/.302/.355
LF: .241/.284/.383
CF: .235/.271/.285
RF: .255/.308/.413
DH: .190/.266/.301
When I look at that, I don't see any reason to believe that Cano or Seager will go backwards. I don't see any reason to believe that Cruz won't be a massive improvement at DH (he was .271/.333/.525 last year; not that far off from his career numbers). I think LoMo has the ability to take another leap forward given the 2nd half of the year last year combined with his age. However, I would agree that it would be prudent to have a backup plan in place given his injury history. I don't see how SS gets any worse next year. I feel like Ackley has turned a bit of a corner so I would expect the numbers at LF to see an uptick. Austin Jackson's career splits are .274/.336/.402. Anything even remotely close to that for 2015 would be a MASSIVE improvement over what the Mariners ran out there last year. In RF, you have a platoon situation set up where Smith has a career stat line of .277/.358/.481 against RHP and Ruggiano has a split of .266/.329/.508. Those stats are a massive improvement if career norms are approached (particularly in getting on base and power). Finally, I think you have a strong case to see Zunino take a huge step forward in the next year or two. Getting a solid backup is definitely needed.
I get what you're saying about Felix potentially regressing, but I expect to see another strong campaign out of the King given that he felt like he got slighted against. A motivated King is a vicious animal. I agree that there's reason to have some concern about Iwakuma. I'd feel much more comfortable if he was the 3rd starter. Paxton's biggest issue will be staying healthy. IF Walker has turned a corner, then that's going to be a massive improvement. Elias is still a massive question mark to me. He's a league average pitcher to me with upside. Beyond Happ, I don't see depth and that's by far my biggest concern on the club.
With respect to the pen, I guess it's very reasonable to suggest that they'll take a step back. However, they all have really good arms and are settled in what they are doing for the most part. The areas where I worry about the pen are injuries and overwork if the rotation really starts to fall apart.
The one other area where I do think that they have some room to move is that the next generation of talent is getting close to the bigs. Should they be in a position where they find themselves an arm short, etc. as the season progresses, they can trade from some of their minor league strength to secure the player(s) necessary.
When I look at the AL West, Oakland will be taking a significant step back and I expect them to finish in last. I like what Houston is building but they are going to be in a position where their goal this year will be getting to .500. I felt like the Angels played a little above their heads at points last year. They have a lot of guys in their core that are aging and it feels to me like they will take a step back. The wild card in the division is Texas ... but something down there just seems a bit broken.