Imagine having perfected your aiming abilities and you're in a 1-on-1 with someone and you're aiming for their head perfectly. The only way for them to survive it, is being faster than you to aim for your head, move real quickly... or... Prone and you, even when you very quickly aim down, and won't be able to do headshots anymore. If you have full HP, you'll likely still win. But if you had low HP from the start, they'll shoot your feet, or jump up again and finish you off. Without the prone it would've been a perfect kill.
I very much welcomed this prone delay. I feel like it makes sense that you can't jump up again that quickly. Even with the prone delay I sometimes prone myself. If I'm low on ammo and need to reload, I prone, reload and try to fight back. But that's because you don't have any other option. If you're just not quick enough or your aim is not good enough, prone should not be your solution.
#voteYes for prone delay!