That's exactly it. SG has 8 vowel sounds (or 9 if you include the schwa), traditionally A, AO, É, È, I, Ó, Ò, U.

The é/è and ó/ò distinction is something you see in several Mediterranean languages (eg Catalan and Corsican) where the acute marks the "open" sound and the grave the "closed".

É is like "ae/ai/name-of-the-letter-A", but as a single sound (as is common in Scottish English accents) rather than a diphthong; whereas È is more like the sound in "bet/pet/let" etc.

Ó is the hard "blow/throw/no" sound, whereas Ò is more like the soft A sound of Irish, or English words like "fall" and "ball".

Historically, the grave accent always indicated vowel length, and there was some mixed usage of the acute marking vowel-quality only or both vowel-quality and vowel-length simultaneously.

Á was always different. It's a short vowel, and only occurs in unstressed positions. It basically says "pronounce this as a clear A, not as a schwa". It was only commonly used in the words á and ás, to distinguish them from a and as. Now they write à and às, even though À denotes a long vowel, and these are short.
(They justified dropping this on the grounds that it's not normally used elsewhere to distinguish schwa from clear-A. There was a common tendency to denote unstressed schwa syllables with U and unstressed clear-A syllables with A... but the exam board wiped that out as well. Three important phonetic distinctions killed at a stroke.)

_________________
A language belongs to its native speakers, and when you speak it, you are a guest in their homes.
If you are not a good guest, you have no right to complain about receiving poor hospitality.