"only possibility for them" is not "the letter 'y' is silent", which the over-downmodded OP is complaining about. That it's not necessary for shorthand is not the same as being a silent letter.
For example, the vietnamese "chicken noodle soup" is spelled phở gà. It's pronounced something like fur gah. Every native English speaker I've heard (including me) that has seen that term written tries it out first as foe gah. If what the article was saying is true and the letter 'y' was irrelevant in such words, that first attempt would at least sometimes be foe gay - and I've never heard it that way at all.
Regarding 'sla', it's probably not going to be mistaken in context, but 'sla' is also a three-letter acronym that is moderately common - Service Level Agreement.
For example, the vietnamese "chicken noodle soup" is spelled phở gà. It's pronounced something like fur gah. Every native English speaker I've heard (including me) that has seen that term written tries it out first as foe gah. If what the article was saying is true and the letter 'y' was irrelevant in such words, that first attempt would at least sometimes be foe gay - and I've never heard it that way at all.
Regarding 'sla', it's probably not going to be mistaken in context, but 'sla' is also a three-letter acronym that is moderately common - Service Level Agreement.