But you clearly can look at it from the other paths it is not kinetic different choices have different outcomes. Have you never played a game with different paths some times characters act different on different paths.
I think you are absolutely missing the point on what people are telling you.
Consistency of people's character has to be done FOR ALL ROUTES AND CHOICES. This is basic in any game and writing.
It does NOT matter how different the solo vs the harem path are. Just pick the harem route on its own, abstract yourself from the other paths. Seriously, just focus on that. Then it becomes obvious that character's personality is pretty much broken in that path. This is a problem for the novel regardless of what is happening on the other paths.
EDIT: sorry, explanation got a bit technical. It is hard to let the academic training out sometimes.
IDEALLY, following a causality argument, you would like that different paths in each novel are consequences of choices that make sense. Say that before making a decision, choosing between A1 and B1, you reach a state of the story called X0. In one path Lisa character dies because MC did something that: MC did A1 over B1, which generated A2, then A3... up to A10 in which Lisa dies. All events are essentially a consequence of picking A1 over B1.
X0 -> A1 -> A2 ... A10: Lisa Dies
If MC had picked B1 over A1, then the sequence of event do not happen and Lisa stays alive.
X0 -> B1 -> B2 ... B10: Lisa survives.
That is, X0 can lead to A10 or B10 depending on whether you picked A1 or B1 by causality. That is, if you want you can think X0 has two arrows, one that leads to A10 and another that leads to B10. A single graph.
Some novels fail to successfully write the causality. Fate Stay Night, for example, has paths that feel almost like totally different scenarios. Where even some characters exist or do not exist but that are NOT a consequence of the character's action in a causality kind of way. It's more like you are choosing parallel realities when you make choices, instead of being lead by CAUSALITY what separates the novel. HOWEVER, inside each path, there is continuity going on. That is, if you take everything from X0 to A10 or X0 to B10, the story does not feel broken.
Instead of X0 having 2 arrows leading to either A10 or B10, it feels more like you have 2 different graphs, one from X0 to A10, and another from X0 to B10.
NOW, the problem with the harem path is that even forgetting the other paths exists, the behavior of the character is broken. Continuity on a single line of the choice tree is by itself broken. You pick A1, then you generate A2, A3... up to A10 but instead of reaching A10, somehow you are reaching C10. Now, C10 contradicts all that X0.
So your path from X0 to C10 is broken down. A10 should follow from X0, but something feels absolutely disconnected, and you reach C10. Notice that picking B1 here has nothing to do with the problem mentioned. X0 to A10 by itself is broken. So forget about that B elements.
THIS is the problem with the harem route. X0 here is the personality of the characters. When you get to C10, nothing happened from A1 to A9 that can justify the personality of the characters in X0 to jump to C10. They were written for solo path (A paths) and now are all happy-go-harem (C).
This disconnection between established elements is hard to tolerate for anyone that cares slightly about writing being consistent and is not just wanting a single outcome.
DEUS EX MACHINAS, if you will, generate the same ugly feeling, where everything is written leading you to to A10 but they invent some random crap that makes you jump to C10. While causality there is not broken BECAUSE of the Deus Ex Machina, it feels like writer fucked on everything they had written before. In fact, you could even set up the harem route like a deus ex machina. "And suddently, a god that was watching the confrontation between the Love Interests and MC felt pity on MC and used his godly powers to make the Love Interests happily accept harems." ABSOLUTE BULLSHIT.