relied on fanservice and lewd "accidents" to entertain.

That's how it got there

I know shows like this (fanservice, romance, lewd interactions, etc) are popular but I rarely see one get to the top spot like this.

I recall that Ishuzoku Reviewers was 1st place in some weeks as well, you may severely underestimate the power of horny in a mostly teen and young adult audience.

Yeah, I was surprised as well. It's important to remember that AC is just one audience though. Alya ended up #2 on their most anticipated list. So, I guess it delivered what AC was looking for while Oshi no Ko must not have to the same degree.

I am curious if Alya will stay on top as the season goes or whether the audience moves on.

That's a really good question. From looking at the rankings for different sites for a little while now, I think that AC tends to be a bit biased toward romance. For example, last season saw Date a Live near the top of the chart most of the season while it wasn't on the other charts (reddit karma or Anime Trending).

Looking at the reddit karma for this past week, Oshi no Ko is running away with things with about 2x as much karma as Alya. Other shows are higher up as well with solid showings from Spice and Wolf as well as Slime.

Oshi no Ko and Tower of God are probably my most anticipated. Pseudo Harem is one of my favorite manga, so I enjoyed the first episode a lot. Out of the other premieres I have seen so far, probably Dungeon People was my favorite.

The true wildcard this season is going to be Nokotan.

Dungeon People and Parry Everything look like they'll be pretty good, but otherwise, I agree