There is no indication whatsoever that as a whole group or a set of people by default will not go to paradise. None. We do not have that knowledge, neither is it in the Qur'anic text.
People like to call themselves names when embracing a theology or insulting it. When embracing Islam people announce their "I am muslim" loudness, and insulting it people announce "I am an infidel". But its not that simple if one educates himself in the theology. There are places where people are called "polytheists" and they will be condemned, but if one reads the Quran, in a particular situation where a set of people have broken a treaty, which is a trust broken, and is a worship of themselves and Gold, it is called polytheism in the Quranic context. If you worship your own ego/wishful thinking/desire which is called havah is called polytheism in the Quran. Thus, based on that context, a peoples leadership that breaks an oath is called polytheists.
What some atheists (not everyone because there are true atheist scholars) do is they pick one verse, ignore the context, and call themselves "polytheists" and make claims like "Islam hates us by default".
So that's false, but common.
Yes. Atheists also will be in this so called paradise. And of course, Muslims will also be there. Not all. Hopefully, most. And that is my opinion. Since there is no indication in the Quran that all of those who call themselves Muslims will have salvation by default. None. I can call myself a Muslim just to get a job or be in the mob. I could be an atheist in my heart. There are many like that. Also Vice Versa.