I believe compared to the rest of the league Dortmund are in a similar spot as Bayern were before they started to spend big every season. Especially their squad depth is unheard of for a Bundesliga club (other than Bayern). I seriously doubt any of the other teams will be able to touch them as long as nothing extreme happens.
Given that every one is fit Schalke easily have the third best squad in the league. And that's with tons of youngsters who can make the next (couple of) step(s) at any moment. Their coach and management prevent them from touching Bayern and Dortmund but they still have enough quality to collect their points against hte rest of the league.
Leverkusen are uncertain at the moment. They have a new coach I don't really know all that well, with Brandt, Öztunali, Son and Calhanoglu they have a good bunch of youngsters who have the potential to be top players (in a league context). How will Drmic adjust to a bigger club? How good will Kießling's season be? How good is Wendell?
They should be top 5 at the very least, but with all their variables I could see them getting into top 3 aswell.
Wolfsburg apart from really needing one or two strikers have a very solid squad. But I think they might lack individual quality upfront if Arnold and Perisic don't make a big step foward. Also I think they lack a creative CM. Even if all of the above does happen they still lack squad depth. I see them as no 4-6.
Dortmund certainly have more depth than the other clubs (bar Bayern) but if you continue with your analogy, you could see Bayern in the past stumble in the league when they went deep in the DFB Cup and CL and other clubs who were not in this position where able to challenge them.
You just have to look at the last 2 seasons. 2 years ago Dortmund finished just one point in front of Leverkusen and last year they only secured 2nd place on match day 31. Admittedly they had unbelievable bad luck with injuries last season but they'll also miss Reus and Gündogan at the start of this season and if Sahin will be fit for the opening of the season remains to be seen. It also wouldn't surprise me if Bender and/or a defender picked up an injury at some point this season.
I think Schalke's squad is a tad overrated. There are many question marks IMO.
You already said that their coach is not not top notch (I think Hecking and a lot of other BuLi coaches are better).
They have plenty of depth in defense but apart from that...
Goretzka and Farfan are out injured which leaves their midfield as thin as the other clubs who contend for CL places.
They have Neustädter and Boateng with Höger and possibly Kirchhoff (both meh) as backup in CM/DM.
Behind the striker they have Meyer (wil he be able to continue his developement?), Draxler (will he come back better after a rather pedestrian season?), Sam (who only ever played one good half season at the age of 26) and Choupo-Moting (who's still kind of raw at 25).
The rest (Clemens, Barnetta, Obasi) are really nothing to brag about.
Up top they only have Huntelaar. Can someone tell me why did they let Szalai go (genuine question)?
So, sure they have the numbers but I think a lot of Schalkes starters are rather young and inconsistend and the bench is not all that great. Did I also mention their mandatory drama at one point in the season?
Agree mostly on Leverkusen. I think they are solid in the CB and DM department.
Further forward it will be wait and see I guess. They basically only have 2 proven players there with Kießling (who is at least an above average striker capable of >=15 goals a season) and Castro. I'm excited for all the other young talents (you named them), I'm just not sure that they will be consistend and be able to function as a team right away.
Regarding Wolfsburg: If they don't buy a quality striker (and I'm talking about a guy who can give them ~18 goals) they probably won't be able to get 3rd. I'd say 4th or 5th in that case, but I think the difference between them and Leverkusen and Schalke is that you know what you get.
They have a good coach. They added a proven 27 year old who was a leading figure at Bremen in Hunt and a good 24 year old RB in Jung.
The only questions I have is if Arnold and Knoche can continue or improve and if Perisic comes back as good as he was in the WC after his injury.
I think consistency and lack of CL can be a real advantage for Wolfsburg over Leberkusen and Schalke.
Also, does anybody know if Schalke (after Szalai left) and Wolfsburg (after Lukaku didn't happen) are interested in any strikers?