Almost every deck I've ever made in Keynote cannot be replicated in PowerPoint. It doesn't have the same support for transitions that Keynote does. Good transitions (not flashy ones) are what make a good presentation great.
Consider perhaps the most famous presentation of them all - the iPhone release - I don't think the slide transitions got too much press, and I don't personally recall what they were.
These days my slide transitions are simple - slide 1 replaced instantly with slide 2. In other words no transition at all.
You may prefer a different transition, but to say it's the transitions that make the presentation great is reaching imo.
I get paid to make presentations, I've worked with other paid speakers, and I've seen 1000s of presentations. All the people who get paid to make presentations use transitions (and almost all of them use Keynote too), and there is a reason. Because it just looks "unprofessional" when you don't.
This book really upped my presentation game, and using transitions is in it with more explanation, if you're really interested:
Yes, you need good content and a good speaker as a baseline, but assuming you have that, the deck is what makes the difference.
Conversely, Keynote was and remains an app designed for visually heavy presentations, so it optimises a lot more for aesthetics: gradients, blends, transparency, (sadly still no blur wtf), animation of items on a slide, very complex animated reveal and build, complicated slide transitions, etc. It has also UX optimised for visually precise layout (in areas PowerPoint is frankly unhelpful).
If you just want to make people look at pages after page of charts and graphs that should have been memos, PowerPoint is good and possibly stronger. If you want to make an aesthetically compelling visual presentation, Keynote will get you there for less effort.
In the real world, where PPTs are created and shared for presenting information and making decisions, we need good integration of real data. PPT does that by linking directly to the source file. If you have an Excel chart that you copied over to PPT, updating the numbers in Excel will update the PPT chart in real time as well. This was a gamechanging feature that saved a lot of time, and I think it only became available with PowerPoint 2007.
Also it exports to video. Which I think Powerpoint doesn’t do? (Older version at least)
Steve Jobs presentations always made use of it.
But I gotta admit PowerPoint has come a long way and has a ton of great features these days too. Eg it can actually.l design slides for you, quite tastefully on the new 365 version.
It was made for Jobs' keynotes as its main goal
This is definitely a YMMV situation.