There is a perfectly good phonetics alphabet, used in dictionaries, so it's only complicated to explain pronunciation if you use bits of "normal" spelling associated with the way you yourself speak, as others may not share that spelling associated with that sound.
A lot of the consonant clusters are simpler than they look, and very few people pronounce every letter in every word when speaking English. I do remember having a bit of innocent fun when teaching English to see how hard it was for speakers of other languages to STOP pronouncing "wasps" or "crisps", as the "sps" tended to continue repeatedly.
However after learning (and teaching) French, German and Welsh I'd dispute that English is any more difficult ... and that's before we get on to some African languages, some Indian languages, Dutch, Russian, Finnish and so on.
As to the way we say "glimpsed" - that's not a mistake of any kind, that's the way we say it. There are quite a few past tenses where the same thing applies. And spelling rules are not pronunciation rules of any kind, after all.
But yes, one of the skills of writing sing-able songs is making sure they can be sung. Not necessarily by speakers of other languages, though!