In medium-large companies, work and promotion are about showing off. Even if you do real work it's more important to be noticed than to do it.

In that light, I don't understand how you and the OP could consider that it's preventing to do real work. Powerpoint is the real work. And it shouldn't be difficult to justify spending 1-2 days on it, with 100 people assisting to the presentation as witnesses, unless your manager really doesn't want you to give presentations (it's showing off your team so it's good for your manager too).

I get it that it's not part of the engineer mindset of course. If I have to give some advice to strong engineers who do good work, that would be to take credit for your work.