I find classroom delivery with PPt so constraining, especially its rudimentary navigation ability. (I guess if you are presenting a linear, read a book type of presentation, it is useable. In that case, I prefer to just copy the book and project the images.) But for anything else, I project my screen from SL (it is, after all, just a webpage), and talk to the audience. I can just lecture and make all the choices, or allow audience input as much as I prefer. If you have the ability to project a PPt, you can equally as well project published SL.
If you have clients or SMEs that want to change the content, they will need to have SL to republish it. If they aren’t interested in that, perhaps they need to be sold on the benefits of using PPt exclusively, without the added cost of SL. It does have some small navigational ability.
If you are willing to present with PPt’s scaled back capabilities, another option might be to also use PPt for online presentations, too.
On the other hand, if your live presenter wants to use audience input as part of the presentation, that can be done while projecting the SL project.