The limitations depend on which program you're using - there's more than one - which is why I only gave a simple example. And if you have to pay for a function that is otherwise free to many others, that's a limitation.
Side loading is installing an app from anywhere but the official store. So by definition "third party" is side loading. Whether it's another store or authorised is irrelevant.
Youre not getting it. The developers of the tools can and do impose their own additional limitations. They're still limitations of the programs which is what we were taking about.
And it doesn't matter what limitations Apple imposes in its walled garden, their phones can still be jail broken and side loaded in the more traditional way.
The concept of sideloading is a general term that applies to multiple platforms, not something Apple owns or gets to dictate. No one is making up anything here.
https://www.twingate.com/blog/glossary/side-loading
https://dictionary.cambridge.org/dictionary/english/sideload
https://zimperium.com/glossary/sideloading
Etc.
If your argument requires cherry picking, ignoring key points, and baseless ad homenims, it's not a good point.