This is where you lost me.
The writing is occassionally weak, and thus it pales in comparison to more younger fantasy productions like Battlestar Galactica reboot, or Game of Thrones. But at it's time it was groundbreaking.
The moments of epic were really good since they were preplanned and they could be foreshadowed much in advance. Hence moments like (spoiler alert...)
... Earth falling into totalitarian state, bombing of one of the alien homeworld, the Shadows overwhelming Centauri prime, etc, were nearly unheard of narrative high points due to the buildup to them over the series.
There were lot of not-so-high quality filler episodes and so on, which make the series more of a cult classic rather than ... an obvious classic.
And yes, I categorized space opera as fantasy :)
At minimum, every episode at least advances a core character. And usually has one Easter egg related to the overall plot.
As you said, compared to TNG, early DS9, or X-Files, this was groundbreaking stuff on broadcast TV.
Yes B5 had some painful filler episodes and the acting was both amazing (G'Kar, Londo, Delenn) and at times bad, but overall the show is the one show that has stayed with me since Kindergarten. Just like TNG episodes (the drumhead and measure of a man) served as mini courses in morals, ethics, and philosophy for kids, Babylon 5 was the same, but more memorable to me as the arc was 5 seasons, two spinoffs, and like 5 TV movies. I learned all about politics, facism, standing up for what's right, leadership, really cool spaceships, the impact of discrimination, and diplomacy (kind of :)). A great show to watch at an impressionable age.
The best part of Babylon 5 (besides the best writing in all of SciFi) was how asymmetric the races could be (makes perfect sense). Earth is pretty powerful among the younger races, but we're nothing compared to the mid-level Centauri Republic & Minbari Federation. We still have to spin mass around our ships for gravity while they've figured out a way around it. So you see the Minbari ships being beautifully designed on the outside and inside (proper living spaces), while Earth ships are almost like old Navy battleships but in space where everything is cramped and people have to where seatbelts in combat as it is so likely for the gravity to be unstable. The ancient races don't even really need to open jumpgates to go into hyperspace, they just phase and have 100% sentient organic ships.