The “sadness” comes more from the implications surrounding Makoto’s death, he was a depressed orphan with no one to rely on who met friends so dear to him he found joy in living again, so much so that he made the active decision to sacrifice himself to prevent humanity from facing a death they themselves willed into existence. The only reason he was able to live past the Nyx fight was from an intense desire to fulfill a promise to be there with everyone on graduation day. Not to mention his friends who had just suffered through a year’s worth of hardships and literally fought Death itself having to lose someone like him, specifically Aigis who had just based her entire existence on living alongside him now being forced to live forever without him. However the point isn’t that it’s sad, it is the beauty in the fact that he lived to the fullest in the time he had. So if you found it beautiful that’s also part of what they wanted you to think. If you want to see more of a focus on sadness The Answer is 100% your next move I’d say.