Iori is actually a 優しい person, even if he himself doesn't agree. I think this ending proved that point. It's great to see the friendship developed between Iori and Saber throughout the story. It's a very beautiful and touching ending.
IMO your interpretation is too pessimistic. It's an amazing ending true to the Fate spirit. Very beautiful and touching. I think it's bittersweet for Saber, but not in any way negative at all. Iori fulfilled his wish of challenging the peak of the art of swords. Saber got somebody who understood him. Both of them became a really good friend of each other as the story developed, and they could be satisfied how it ended like this, as you can see when they lay on the ground next to each other. As of Kaya, Iori explicitly said that she's smart and strong and doesn't need Iori by her side going forward. She also has a whole family behind her. She'll be alright! In fact, I think worrying too much about Kaya in this ending is a somewhat self-important and presumptuous attitude to take. If Kaya knew the truth (which she might not), she would be relieved and happy for Iori that Iori got to live out his dream and die happy.
I don't agree. Iori explicitly said that she's smart and strong and doesn't need Iori by her side going forward. She also has a whole family behind her. She'll be alright! In fact, I think worrying too much about Kaya in this ending is a somewhat self-important and presumptuous attitude to take. If Kaya knew the truth (which she might not), she would be relieved and happy for Iori that Iori got to live out his dream and die happy.