My two cents
Sometimes presentations become Frankenstein monsters.
They are made of several parts that don't fit together anymore, and too many people have worked on them, and now they are all messed up both in the design and the storyline. Worse you might still have dozens of comments in them that need to be addressed.
How do you get from that to a presentation that works, with a clear story and a clean design?
Step 1: do a content audit
What I'd suggest is to not work on the individual slides, but rather to something that we could call a "content audit":
Go through all the slides
Each time you see another type of slide type, draw on a sticky note what's the content structure (like a wireframe).
Don't focus on content so much but more on structure. For example a slide that has a "graph + text", is basically the same thing than a slide with "an image + text".
Step 2: Rebuild the story with sticky notes
Once you have your content audit, you can now rework the structure of your presentation. Don't do that in Powerpoint, Keynote or Google Slides, but continue to work with sticky notes.
Basically, you can write the title of your slide on a sticky note, and below show what "structure or wireframe", that you've found in your content audit, would work best.
If needed, you can add below another sticky note with the thing you need to change in the content, based for example on the comments that you haven't already worked on that are still in the presentation.
Step 2: Build your lego blocks
Now you can go back to your presentation app. Because it's time to turn the structures or wireframes you detected in your content audit into reusable lego blocks or templates. Just make a copy of your old presentation and add the templates or lego blocks at the end of your presentation.
Step 3: Rebuild your presentation like a machine
Now replace your old presentation with the new templates based on your new structure. But don't do that slide after slide. Instead, do it template after template. For example, start by changing all the "Title 1" slides. Once you're done with the "Titel 1" slides, change all the "Titel 2" slides. You get the idea.
It just feels good to be like a machine that spits slides! Plus you can tell yourself! Nice I've already done all the titles.
Here I recommend that you keep the more challenging slide structures for the end, to help build the motivation at the start.