Thanks for the help! I completely forgot you could use older versions of TF2!

In fact I found out that it is simpler than I thought, since TF2 has a beta version called "pre_smissmass_2022_demos", which was literally made for this very purpose...

So for anyone else wondering about this issue, just select the above mentioned beta version of TF2 and you're good to record older demo's.

My problem is that people's ragdolls simply don't spawn with cosmetics upon death while I'm playing a demo file. This issue has been tested with both first person and STV demos.
Ragdolls work fine while playing a live game, so this must a demo related issue...

A friend of mine suggested that it could be caused by some recent TF2 update (probably within the last 3-4 months, since back then he wroked on a project where ragdolls worked just fine).

So does anyone have a solution to this or maybe knows the cause for this?

Don't make second demo or solly in the game and DON'T replace airblast with anything, airblast is maybe the only one thing really skilled to do as a pyro and if it will be removed, everyone will hate pyro for doing w+m1 even more. And pyro has already some jump weapons like detonator or scorch shot and even a reflect jumps so i don't see any point for adding something else for jumping. And as you've said pyro is already the class that can flank, ambush and mainly defend. If you want to add some new ability for pyro, it might be some ability for melee weapons (volcano fragment or back scratcher).