I didn't even realize Keynote had a latex engine. The equation support in Powerpoint results in nice formatting, but Powerpoint doesn't directly support latex format without third-party addins so it gets a bit tedious to use for more than a one-off. I generally end up using the equation editor in Word (that does support latex[1]) as a workaround, and just copying the output into Powerpoint.
My experience of the equation editor in Word on MacOS is that it definitely does not support any meaningful degree of compatibility with TeX. Command-alt-E in Keynote works properly and seems to have most of amsmath imported by default: you can \begin{pmatrix} or \begin{cases} easily.
One of my worst weekly experiences is receiving documents in Word, especially papers written by colleagues with maths in them. Writing Markov chains in the supplementary methods section for a recent paper genuinely drove me to distraction; each non-ascii character was a major break from the flow of the sentence and requires a move to the mouse.
I really dislike Word in general, actually: on Linux (my workstation) LibreOffice is integrated well and polished; on MacOS it isn't as much as there's some value in having the 'real deal' product as administrators in my university use it a lot. I don't understand why Word's behaviour is interpreted differently from that of the rest of MacOS: e.g. in Word, clicking to select a chunk of text from the middle of the word automatically selects the whole word the cursor was in, unlike the rest of MacOS. This makes selecting parts of a word almost impossible, and it's not possible (AFAIK) to turn this behaviour off.
Will have to give Keynote a try!
[1] https://support.microsoft.com/en-us/office/write-an-equation...