@KazumaLee94: You bring up good points, but there's still a few things I think you got confused:
"I am well aware that this is partially a slice of life manga, however this is mainly a romantic comedy manga."
It's actually the other way around: It's mainly a slice of life manga that is partially a romantic comedy. After all, in the end while we are seeing Amano and Manabu's relationship, we've been mainly seeing Amano in her day-to-day during, or after, school, at Kendo, around the house, or with her friends. The synopsis is originally focused on Manabu, sure, but the mangaka made it clear the story is focused on Amano. That's their fault.
"So what if the story is "slice of life", that shouldn't mean that the romance (which is advertised as the main focus) should be put on the sidelines."
That's exactly what a Slice of Life manga means, though. Also, Ore Monogatari and Lovely Complex are both Shoujo manga and this is a Shounen, so that's not a fair comparison. Shoujo are much more romance-focused since it caters to women-readers and Shounen focuses on male-readers who prefer reading more action. So the mangaka's excuse is pretty obvious: They're catering to a generally male audience who don't really care that much for romance and focused more on the ecchi. It's not hard to create romantic moments that gets the characters hearts pumping, but as for story progression, slice of life will almost always make story sit on the sidelines.
"It gets very repetitive."
Not disagreeing with you there. Actually most Slice of Life manga are like this. Though I think you're more focused on Shoujo than Shounen (I'm the opposite), so as someone who typically reads such things (Nisekoi, Yuuragi no Yuuna, Bokutachi wa Benkyou, etc.), Slice of Life always gets repetitive with their characters. Again, it's more about their interactions than actual progression. As such, while things get repetitive, sure, it's all about enjoying the present and not worrying about what will happen later, like most manga.
As for Amano's friends, they're actual supporting cast. They make an appearance so we can take a break from Amano's shenanigans and see something different (the commercial break before returning to the show, if you will). Some people like them, some don't. To be fair, though, I'm not pulled by them either.
All in all, you've made a lot of comparisons to Shoujo manga vs Shounen manga. I think that's the core of your mistake. You've been comparing an apple to an orange: They are both fruits (Slice of Life manga), but one is sweeter (Shoujo) and the other has more kick (Shounen). All in all, you're views are on point if this was a Shoujo (Seriously, dude, what you wrote was well described! Kudos!). But because you're reading a Shounen, same rules don't apply.