I'd say there's a line between the tone and depictions of berserk and AoT.
AoT, at the end of the day, is just a gory shonen. A incredibly rough and predictable one, at that. It's the kind of series where you know that the main characters will come out as unscathed as they were at the start. No major losses beyond a few expendable side characters and maybe those villains they want us to feel bad for. Eren's protagonist powers will save the day, Mikasa will fuck her brother, and hopefully Armin will be transported to a more deserving series.
With Berserk, you're with Guts for such a long time through his journey that you see him at his absolute lowest, such that ANY improvement to his situation makes you feel better for the guy, even if it gets negated by future events. The fact that the guy has actual comrades and a glint of hope towards treating Casca is a massive improvement over how he's been in the past, even if he likely will never be getting happily ever after. in other words, it's the act of wanting but knowing otherwise that makes the difference here.
but hey, I'm horribly biased towards berserk and horribly biased against Attack on Titan
so you know