Yes, the first four states splitting evenly between the current top four candidates is probably the worst case outcome in terms of not coalescing around a single leader before super Tuesday.
But even in that case I think the field would still have narrowed down to those four. I can see your reasoning for why Harris and Klobuchar would stay in until their home states vote, but I think the x factor you are missing or under weighting is money.
In 2008 John Edwards won 26 of the 137 delegates up for grabs in the first four states (about 19% of the total), which is higher than you are guessing Harris, Klobuchar, or Buttigieg will pull down. The race was wide open with neither Obama or Clinton having an obvious advantage at that point, and if Edwards had kept at that same level of support throughout the rest of the primary he would have been the kingmaker at a brokered 2008 democratic convention, no ifs, ands, or buts about it. The reason he dropped out before super Tuesday was that donations dried up once it became clear he wasn't going to win the whole thing. It's really not much fun to be running a presidential campaign once the money dries up. Sanders (and maybe Yang) has dedicated enough supporters I don't think they'd stop donating even after disappointing performance in the first couple of states, but I don't think the same is true for any of the more conventional democratic candidates which is why I think we will see rapid consolidation among the rest of the field after Iowa and/or New Hampshire.
Harris has been
laying off staff and closing offices in NH for almost a month now. Her campaign is clearly running on empty, and she's prioritizing keeping the Iowa offices open over NH. Realistically, if she doesn't break the top three in IA, she's going to drop out rather than deal with the embarrassment of not having the staff and resources to compete in NH, NV, and SC.
Klobuchar doesn't appear to be in quite as much trouble financially, but as far as I can tell her campaign up till now has been focused entirely in IA and NH. She only hired a political director for NV in the last week and says a hire for SC is "coming soon." She raised less than $5M in Q3. (Warren and Sanders each raised more than $20M in the same time frame, Yang, Harris, Biden, and Buttigieg each raised more than $10M.) If Klobuchar doesn't win at least one early state contest she's not going to have the money to compete past SC, and realistically, if she's going to win any of the early states she'll win Iowa, so losing Iowa may be enough for her to call it quits.