Yeah, ignore the previous demos, go learn strafejumping and soon you'll be able to get past those rets (and lots of other things) with ease every single time (unless you mess it up). Don't even need a good starting position.
For learning strafejumping I recommend the map straftrain1. You just need to jump continuously (pressing and holding jump before landing the previous jump, then releasing and repressing after each jump), hold fwd+left and look about 35 degrees left, then suddenly switch left/right at start of each jump, so on 2nd, 4th etc jumps you hold fwd+right and look ~35 degrees right. The optimal angle approaches 45 degrees as speed increases.
You'll also want to use Options->HUD->Show Speed: "Text + Graph No-Z" so you can see if/how fast your speed is actually increasing.
If that takes too long for you, you could just wallwalk only at the very start past the corner into ret range, then drop on the ground and run past the side of the rets. It takes longer and is easy to get stuck, but may be easier if you can't strafejump.