As a person who has made a living with MS Office products throughout the B2B sales cycle, I am fundamentally grateful for the tools created. PowerPoint is extremely powerful. Unfortunately, the one thing it "needs" the ability to do - train people how to use it effectively - isn't really a core competency. Practically speaking, I don't think instruction on how to use PowerPoint is genuinely possible, insofar as different business and cultural applications will have varying approaches and implementations.
The only thing that bothers me about PowerPoint, on a personal/professional level, is that it is so easy to use. Any semi-literate person with an ojbective and enough time on their hands can realistically create a deck. In a lot of ways, I see PowerPoint and Garageband as similar in this regard - sure, the software can help "make" a presentation or song, but will it be any good for an audience?
Basically, I think your first point is spot-on, and should be used as a buffer from undue criticism. In my professional experience, I've seen far too many "experts" in their fields try to tell me, the "presentation expert" what to do, how to do it, and be stupidly stubborn in fighting the collaborative process. To put it another way, many professionals talk trash about a liberal arts degree (such as creative writing) or the pursuit of experience in live performance (such as drama or comedy in front of audiences) until they realize that the highest stakes business situations are simply concentrated, higher pressure versions of those types of performances. It takes quite a while for a professional to get to a point in their career whereby they might have this epiphany, and those who do "get it" rise to the top in competitve opportunities. They understand the art of presentation, and they embrace guidance and support from artists (wordsmiths, graphic designers, etc) to achieve their vision.
My thesis topic for a Masters in Education (Curriculum Design) focused on the balance of technological tools versus internal intellectual development. Somewhat akin to the hypothesis of "If I have this ubiquitious computer program that will correct my spelling / grammar for me, do I really need to know how to write well in the first place? No!" From what I found in research / studies, yes, that appears to be the trend.
PowerPoint unfortunately allows its users to fall into the same trap, insofar as people can fire up the program, get started, and plow through to their objective ("create a presentation") without the due diligence to plan, structure, and consider their audience's expectations and attention span. That's not the software's fault...well, maybe in some respects because it doesn't have the hard learning curve to keep it out of the hands of those who shouldn't be diddling with it (Garageband vs. Ableton Live is a reasonable comparison), but there's nothing inherently bad about PowerPoint. Nope, it's a good piece of kit. The idiots that use it on the other hand? Yeah, software can't fix them, nope, no way, no how...
Now, if you'll excuse me, I have to go back to deleting 17 extra Master Slides, adjusting page numbers so they all align, re-pasting graphics from Excel as Enhanced Metafiles instead of JPGs, fixing the header font size to be consistent, and wondering what kind of demon decided to change the font from Arial to Calibri in random places!
(Not really, but been there, done that, got the T-shirt)