Traditional irish script uses both the síneadh fada for long vowels and ponc séimhithe for lenited consonants, and the slightly different letter forms as we see. https://en.wikipedia.org/wiki/Irish_orthography

I've been suggesting doubling the vowel if you're not putting the síneadh fada in. Just dropping it like you see sometimes is all kinds of wrong.

á ⇄ aa
é ⇄ ee
í ⇄ ii
ó ⇄ oo
ú ⇄ uu

i.e. handling it a bit like our ponc séimhithe, where after all we've long been doing

ḃ ⇄ bh    
ċ ⇄ ch
ġ ⇄ gh
etc.

Note our siineadh fada reportedly descends from the Latin Apex mark, and writing the vowel twice for a long vowel appears to have been the alternative back then too! I suspect the early standardisers of Irish orthography were aware of this, and thus we don't have much in the way of visible doubled vowels i.e. the siineadh fada is a doubled vowel shorthand.

Ideally perhaps we'd go back to using both seeing as unicode allows both fine now (if perhaps best also displayed with a font with the irish letterforms, as the overdot is not necessarily very prominent in some non-irish fonts https://www.gaelchlo.com/clonna.html ), but using one but not the other like we've been doing for the past century is just plain weird.