Of all the songs I chose not to include this song in my customized version of We Can't Dance which removes the songs I personally consider filler, this is easily the best. While Never A Time is just Throwing It All Away but worse and Hold On My Heart is just In Too Deep but more compelling, Since I Lost You is a song which objectively has nothing wrong with it. You could argue it suffers from sounding too much like solo Phil but not enough like Genesis, and I wouldn't disagree that it might sound like that, I would argue it's a better Phil ballad than anything that came after his first two solo albums. That chorus easily could have sounded whiny as fuck if Phil decided to phone it in, but as you said, he's ace in this song.
I don't know that Peter could never do a song like this, but he definitely never would. Pete always lacked the confidence to scale back on the music and let his voice take command in a song meant to evoke these emotions. He's flirted with it sometimes - Don't Give Up sort of tries this and fails, the more minimalist live versions of Here Comes the Flood do it with more success. He could probably knock the chorus of Since I Lost You out of the park, but he would never touch those verses.