That’s not holding back browser development, that’s just holding back browser usage.
That’s definitely not the same thing.
Kind of a strange semantics argument at that point. Saying you can only build with X tools certainly impacts development. Why develop something that would never be allowed to be released?
That’s the exact argument you’re making: that X tools are the only way to develop a browser. Ignoring the entire world of other devices available.
If you are only allowed to use internal combustion engines how do you expect to get an electric car?
If you have no where to sell your product, why develop it?
It has nothing to do with usage. It’s a restriction that’s imposed on the browser developers.
Mozilla themselves claim that this makes development harder for them.
By forcing developers to have the same limitations as their own browser, apple has made it difficult for competitors to gain an edge over safari.