The elbows are mainly there to lower the pipe opening so it can't pull air with a vortex, quite important when using side mounted bulkheads as the top edge is usually pretty high up. It might not be an issue at the bottom of 2+" of water, but that depends on the size/flow i think.
The reason for tees, caps and elbows is to be able to open the cap on the tee and shove a cleaning snake down the pipe... not that i have ever thought about doing it, even though i did allow for it even in my build. With open pipes as it is that doesn't matter, you could shove a snake down anytime.
I think it might be harder to tune the open channel level with a flat cut vertical pipe though. With a tee and elbow or just elbow you can raise and lower the water level on the side of it knowing it is changing by tiny amounts. With a flat open pipe once its flowing into it its probably at max capacity before it makes noise as all the walls are running water... Changing the flat cut to a slope might improve it, as you could raise and lower the flow in it by how much of the circumference is flowing. But i haven't had an open channel like that before.
The question asked about how far down all the pipes are from the top is important though, if there isn't enough room to start a siphon on the last pipe then you will have a mess if its ever called into action. Those pixels don't show much though...