Your friend is a moron. Frieren is good because the story it's trying to tell is decent. There aren't many anime that deal with Elvish semi-immortality all that well and go over the issues of what it's like to be a long-lived species around a species of people that live infinitely shorter lives than you. Dungeon Meshi touches on it in the Manga a bit, with Marcille being upset because she outlived her father, and she's eventually going to outlive her friends as well, and discusses how long-lived races view the shorter-lived races as essentially children. But it's not to the same extent as something like Frieren, where one moment you're celebrating the destruction of the Demon King and the next you're seeing that same party as old men.
You get to see Frieren's change from being this stoic elf who kind of ignores others for the pursuit of magic, to a woman who cares about the people she's been tasked with nurturing and guiding. Her relationship with Fern specifically is fantastic, and it's one of the reasons people argue that Fern and Stark are the main characters of Frieren after they're introduced.
The show is also great because it doesn't try to pull the postmodern bullshit that a lot of shows do nowadays, where they go "oh no, the thing we're fighting is definitely evil." It's one of the reasons people liked Goblin Slayer, even if Goblin Slayer is definitely mid.
Friren IS a solid 8 out of 10 anime. It's not one of the best of all time, nor is it flawless and for everyone, but within the fantasy genre, it's pretty impressive. It doesn't help that if you try to read Western fantasy, you're more likely to encounter Romantasy, which is trash. Then, if you're trying to read Japanese or Eastern Fantasy, you're either getting an Isekai story or a Solo Leveling/Gamer story.