Alright, sunshine week is over for E$EA so I have some suggestions. First I want to mention that we got back capped once in all of the games we played and it was not because we were pushing out of last, so that transition between 1 / 2 is fine. The real issue with the map is how easy it is to hold last, we held a lot more than we should have on that last but we also failed pushes into last a lot more often than we should have. Stark's suggestion about filling in the tiled area is actually a really good idea and it's one I had thought about, I would also think about removing secret as I survived being ubered into while playing top left (to force the uber early) by running into the secret and just bouncing players / being ignored because I was not really an optimal target. As a pocket, a lot of the issues I discovered were related to how ubers / pushes handled and the biggest annoyance was actually just getting into last. The top left and top right chokes are actually really small and really short which makes it difficult to get through them without being spammed into oblivion (and therefore getting a bad uber off) or without getting forced by a soldier playing in a spot with very little risk associated with it.
Once you got into the point, it was very difficult to have an effective uber. Typically, when you're pushing into last on even ubers you want to use your uber to force the uber, and then kill the sentry / heavy and then make space for your team to move in. The last's size contributed to making this difficult but this really wasn't an issue for the same reason it's not an issue on snakewater or process. The real issue I had with sunshine last was how safe it was to hold near spawn. When you ubered in, you could typically get the sentry with soldier or demo spam but while you were doing that the medic and demo would run away, but not always by running away from the uber, typically the demo backed into spawn and, in fact, most damaged players would simply back into spawn to get resup. On most maps (gully, snake, process) you punish backing into spawn by standing on the point but because the spawn is so close to the point and because the point caps so slow it would be hard to do that. So, on a typical uber push you could kill the sentry (which there would almost always be because there were way too many 1/2 stalemates which all lasted way too long) and then maybe damaged players enough to force them into spawn and maybe force the uber which all culminated in basically 6 v 6 (possibly the pushing team having a sniper and the defending team having a heavy which made it more difficult) over a barely captured point and very healthy defending team.
I would say pushing out of last is about as difficult as pushing out onto snakewater but I don't really think that's so bad as you can typically countersack / force ubers if you play correctly.
TL;DR last is too hard to push because the spawn is too close to the point and/or the point caps too slow, as a result of the difficulty of pushing last (and to an extent pushing out of last -> pushing uphill) and of the many many small hard to push through chokes that really need to be examined / redesigned in some manner last would often stalemate out resulting in very slow gameplay (in our match vs MLX BLUE we sat on last for 20 minutes or so because it was so easy to defend but not easy enough to push out)