I'm concerned that many people are dropping this manga when they haven't even gotten to the main story, which isn't even revealed until near the end of season 1.

I think a lot of people are prematurely rating this series before they even know what it's really about.

It's quite understandable, most similar series are usually power fantasy, harem or rely heavily on echi so those are the most likely to give the series a chance. If you don't catch on the fact that all is planed by the time hero you might find some things unreasonable.
Also if I'd started now and binged into two flashbacks I would've probably dropped it. (I mean this new season is a bit too slow).

I don't know, I'm reading the reviews and a lot of the low ones seem aware of the twist and still chose to rate it poorly.

The manga Exterminator needs 15 chapters to get to the main point and lots of people think that was too long to set up the real plot. Now, there are other issues with that example that lead to me rating it a 4.6, but most readers of it were pretty forgiving of it and it's got a 7.5 rating across 209 people.

With all due respect, if it took 60 chapters to get the setup done, there might be an issue with the writing due to how long it took to get to that point.

Not to mention the complaint I'm seeing a lot of is, if I may paraphrase, "Yeah, we saw the twist, but that still doesn't excuse what he did."

Or, and this may sound harsh, but maybe people just don't like what you think makes it good. Not saying your taste is bad, in fact, I often review things with a score outside of the norm, so perhaps I'd even side with you. But the reality is, most people don't rate things on logic or consistency.

For proof of this, I refer to Gokufuri Kyohi Shite Tesaguri Start! Tokka Shinai Healer, Nakama to Wakarete Tabi ni Deru

A reviewer, who normally has better sense, claims:
"After 29ch...another shallow isekai for harem loving teens/otakus. Unless you like harem, obsessive chars, forced situations and a overly cliche story, I wouldn't recommend this one....Unfortunately, after that it's just the MC going around knowing girls."

What actually happens is the MC meets more guys than girls, doesn't get romantically involved with the girls (and most of them aren't interested in him that way, either), and then parties for a while with a party before leaving them because they don't want to leave their area but he wants to see the world.

Objectively speaking, the reviewer is wrong. So I gave my review with a rebuttal to the objectively false facts.

And then another reviewer, after I make my review, basically says: "See the objectively wrong person's review, that's the accurate one."

A lot of people just don't use their brains.

I'm a jack of all trades but master of none. Too many jars and not enough hands.