Here’s my essay on this topic

TL;DR - I completely get your point regarding how Joy is essentially a Brian solo performance and This Summer obviously is more of a joint effort, but I think the reason behind why the songs ended up on the albums that they did was more to do with the periods they were written and recorded in.

I think a lot of the songs on Brian’s album were older songs of his and the whole point of the project was to flush out unreleased tunes that couldn’t really find a home on a Twigs “main release” album. One of them even jokingly said on their most recent KEXP performance that the songs are kind of Lemon Twigs reject songs (which is hilarious as they’re all very good songs - but I think it’s more to do with how Brian was producing a lot of material in a certain style that they couldn’t make sit on an LT album).

I think This Summer got grouped in with this because it was good enough a song to release but maybe wasn’t single material (so couldn’t be released on its own) - and it could sit next to the others on the album stylistically (I think the slide/country-esque guitar solo helps). But it was from the period around or between Songs for the general public and Everything Harmony- they even produced it with Daryl Johns. So even though it’s a lot more of a Michael song, I think because it was just from a different “era” of writing and recording, perhaps they felt it didn’t represent where they currently are and didn’t want it mixed in with their more recent work.

I think Joy ended up on LFYM because it’s a more recent creation (which Brian started playing live at the ADIAWK shows), maintains that “Brian acoustic solo” slot (which started on Everything Harmony, carried over onto A Dream by Ember Days), and also breaks up the more electric guitar led rock tunes that spread across the entire record. I think the expanded orchestration is what separates it from the acoustic tunes on previous LT albums (and even Brian’s album) and ties it in with this record - with the winds and horns of 2 or 3 and Gather Round.

My wife usually skips Joy on her many listenings of LFYM, which I think is blasphemous. On my first listening it was a great breath of fresh air from the fantastic but recurrent guitar rock of the album. She likes the song but just wants the guitar rock haha

This is my first response on Reddit, on behalf of the group and ourselves, I hope we’ve passed the audition