Setting your angle through commands doesn't work on tempus yea, but other than that it should work just fine
I was told pitchup/down is banned because it would make angled bounces too easy for soldier. Imagine if we had pitchdown allowed just for demo since stickies are rng, or exclusively allow a value of 360 degrees since it doesn't fix your angle to one spot. Just an idea; I know this is super trivial and might make certain demo jumps cheesable/easier. Also it might cause inconsistency in tempus rules so I'm not advocating for it.
You can use cl_showpos 1 to look at your angle. But you can't use commands to instantly make you look at the ground in the right angle. But if you manually got the angle (will take a couple of seconds) it's fine.
This angle is impossible to get without pitchdown because the minimum angle of 89 degrees is too high up
The other way to downair jumps like these without a wall is to downair non-linearly, but that is harder.
Edit: cl_pitchdown 360 doesn't snap your angle to a precise spot (if you do a full 360, it does reset your aim to a certain spot, but it doesn't let you get a perfect angle toward the ceiling every time with normal sens).