Let’s take the first letter: a. Sometimes it has the pronunciation as in bay and sometimes the pronunciation it has with announce. One symbol, two pronunciations. We might as well say: aaaa aa aa aaaaaaaaaaaa. But it’s confusing right? That’s why we try hard to make it easy to people by having unique symbols for each sound.
When used in bay, it would have been better written as bé, more in line with European languages, as used in Swedish, Scottish and French.
This solves the issue of the pen which sounds like pén but as written should have been pronounced as pin. Interestingly pin should been written as pen since e has the sound as pronounced in leeds.
Leader should have been written as leedar with the a as in action. Some goes for leaf -> leef. The a as in say does not sound.
English is taught by parrot learning. Don’t deduce, just learn it like that. The common first words like house, bed and apple are actually written as haws, béd and app<>l.
There should have been a vowel between p and l in apple, at the very least it should have been appl.
Linguists obviously use something like this: “æp.əl”, which half solves the problem