I believe the old DAL stuff is gone, maybe somewhere around version 30? I used to have awful crashes all the time, either Zoom's capture host process (caphost) would crash, necessitating completely restarting the app, or OBS would crash. Now it just installs a camera extension, so yes, I believe it's all on the CMIO APIs.
I am mostly broadcasting the desktop view of a second or third computer on my desk, plus slide decks, graphics, etc. I hate Zoom's clunky screen picker UI and never want to accidentally share plaintext secrets or PII to the attendees by choosing the wrong window or absentmindedly moving a window to a shared monitor or something, so I got around that by just using OBS as a switchboard, and never having production data on my test computers. One is hooked up to an Elgato Neo capture device over HDMI, the other when required over a BMD Intensity 4K on an eGPU dock. Slide decks are the only data from my presenter computer ever shared, but via a 'macOS Screen Capture' source. I have a few scenes with text only too for info/time stuff. It's great being able to slap some text over a scene, or have two computers up at once in a half-and-half arrangement. Plus plugin support (used to capture from the BMD from a PC tower and send the video to my presenter computer over NDI when an older elgarbo capture card shit the bed), audio and video filters/effects, goddamn shaders, sky's the limit since OBS is so extensible. I've done in person presenting and still used OBS to generate a fullscreen projector of the program output.
I also personally have always found the "presenter awkwardly clicking around through an un-played Powerpoint" to be really unprofessional. I can hide all of that messy stuff and not just a bunch of dead air.
Right now I'm working on getting an Adafruit Macropad to talk to an ESP32 over UART so I can build a wireless streamdeck that doesn't require any shitty bloated control software. The ESP32 would then send commands/get statuses from the Websockets server and send em back to the Macropad so it can update the screen. This would be impossible to do with Zoom since the app isn't scriptable (on macOS most AppKit UI can be automated with AppleScript) and they only engineer for the lowest-common-denominator use cases.