I hate to break it to him but the ISA really is not that important with software development nowadays. This of course is because we don't write our code directly to the hardware but rather to an interpretative layer.
That
really depends on what you're doing! There's a lot of low-level work where the ISA is hugely important. If you're writing performance critical code like compilers, or big-name software video encoders (e.g. x264), or certain parts of game engines, you absolutely care about the ISA, because even if you're not writing literal assembly, you still need to make sure your code is tightly, manually optimized for the processor.
This isn't a huge range of projects, but they effect a lot of other people! Game developers care about having optimized game engines, and
lots of developers want to have well-optimized compilers for lots of different languages.
And sure, Apple could create some of this core work themselves, but e.g. Clang benefits greatly from the work done by non-Apple contributors, and I don't think Apple wants to start supporting their own iterations of Rust and Go and all of the other languages people use. Because Apple is using ARM, those projects can very easily port over their existing ARM code to Apple Silicon. If Apple went with a fully custom design, everything would be a lot harder, and I frankly don't think even Apple would have the clout to pull it off.