the learning curve for Lightroom/Photoshop or Affinity Photo is partly steeper - of course the process of developing photos in Pixelmator Photo requires the same basic knowledge and understanding (Pixelmator Photo has probably the fastest implementation on iPadOS of the function it offers, like single or batch edits, sophisticated upscaling, etc. and it is the best with iPadOS/iOS integrated app. Photo management is solid, but in comparison basic and currently not as extensive as in Lightroom).
Lightroom/Photoshop as well as Affinity Photo offer significant more functions to tune your image locally with functions like masks, ROI selection, predefined Filters - with a steeper learning curve. Additionally when you like to compose panoramas, HDR, want do do local edits, use masks, &&& you have have to choose one or the other - in either case there is a lot of knowledge to acquire. (Just for the protocol: Google’s Snapseed offers a lot of this function on its own, but integration with newer versions of iOS/iPadOS lacks - e.g. integration with Apple’s Files app to access photos directly on a SD card or external SSD or hard drive. But this is high level complaining, I mean it is free!)
The combination of Pixelmator Photo, Pixelmator and SnapSeed offers a lot for a much lower investment in money and time than the other apps mentioned. If you find that you need more I would additionally invest in Affinity Photo and Affinity Designer - of course there is a lot to learn (same is valid for LR/PS) but it enables you to do what you want with a single investment and not monthly costs for a subscription.
I have no professional affiliation with Pixelmator - but, as said, IMHO Pixelmator Photo is one of the best integrated and - surprisingly - most underrated apps on iPadOS.
