Mac user here - I was already using APP and Photoshop when I got Affinity so I haven't started over with it. What I do like about Affinity is that it's 32 bit through the whole workflow. No need to step down to 16 bit as you have to do with Photoshop.
APP has subscriptions (60 Euro for a year) as well as long term purchase options, so that may be an option to get started with it again. When the year is up, it just stops working, so you get to decide whether and when to pay another year, switch to "forever" license or use something else.
Siril is free and works on Mac
Here's my experience with PI. I wanted to explore PI after feeling that my existing workflow had a lot of "playing with sliders"; APP has good light pollution and star removal tools, is great for mosaics, can pick apart duoband images into Ha and Oiii and can export stretched stacked images; however I found the stretched images noisy and stretching in Photoshop takes time and may be error prone.
I think the notorious learning curve for PI is more about learning the workflows and knowing what to do when. As well as that, it has multiple ways of doing certain things in the user interface. And despite having a fairly standard operating system interface on Mac, with normal menus, it has some extra window decorations which are new and different although easy to learn.
I tried various ways of learning PI, but what worked for me was Lukomatico's new tutorial series. The tutorials start with already stacked images, which for now I am continuing to do in APP. This has opened the gates for me to be able to follow other tutorials with variations on the same workflows and pixelmath recipes. https://youtu.be/UKd0pUBSZ6o
And pixelmath - what's not to like, it's magic.
I use NoiseXterminator and StarXterminator plugins; one license works for both PI and Photoshop; I heard that Affinity can use the Photoshop plugins as well.