Once the native engine is available to the general public, there will be more users. When there are more users, there will likely be more resources thrown at development.
The issues in question aren't something you'd ignore just due to lack of a native engine - Firefox on iOS matters for market share reasons, they need to care about that stuff regardless of what's running under the hood.
> Once the native engine is available to the general public, there will be more users.
Why do you think this will happen? The landing page for firefox.com above the fold only makes one claim about "a lightning fast browser", with their selling points being privacy, Firefox View, editing PDFs in-browser, and total cookie protection, all of which are possible in the current WebKit experience. Either Mozilla really doesn't know how to market Firefox, or less people download Firefox if their CTA is "our browser engine is better than Chrome".
Other browsers on android can do that too. Actually, firefox has a fairly restrictive extension policy, while browsers like Kiwi let you install any chrome extension that you want.
I use it as my main browser and only had to go Chrome to open some trash sites (litteral “let me load a bitcoin miner in an invisible element” kind of trash)