I don't disagree with the latter point, but the former doesn't make sense to me; unless you're saying that there wouldn't be enough phonemes representable by the letters to define spellings for all English words? In my mind, the entire point of a conversation like this is hypothetical changes to the language to make it phonetically consistent; of course it isn't right now, or we wouldn't need to have a conversation.
You've correctly identified what my reasoning is, but you seem to be circularly saying that since English isn't currently phonetic, it's impossible to come up with a spelling for it using sounds that roughly resemble the common sounds letters are using today in order to make it phonetic. I guess I don't know that it's literally impossible, but I don't think it's self-evident that it's not possible, and I think it's fairly straightforward changing the spelling of words ending in "le" to "el" would be more consistent to how "le" is used in other places in words where changing their spelling would be more difficult (e.g. there's not really any clear way to spell "less" without preserving "le" at the beginning).
You're definitely right that I hadn't considered that some dialects pronounce "missile" in a way where it's pronounced differently, but I'd argue that the obvious example (British pronunciation) was already basically ignored by the comment I was responding to, so I didn't really introduce the inconsistency.