Back when I was at school in Russia, one spelling mistake in the final examination essay meant minus one mark ("A" to "B", "B" to "C" and so on). From today's point of view, this seems somewhat egregious.
> Especially when the distinction between words and phonemes can seem rather arbitrary in a language full of clitics.
Uhh... Russian doesn't have a lot of clitics. There are compound words like in German, but they are still understandable if you read them phonetically.
And most children learn to read first by sounding aloud individual letters, and then just training to do it faster. It's called "reading by syllables".
But Ukrainian is still even better. It's almost completely phonetic both ways and you usually can write down any word you hear without problems, even if you hear it for the first time. There are still some double consonants and a small amount of reduced vowels, but even they are still somewhat reflected phonetically.