I am not an expert, but I believe that Ulster Irish always puts stress on the first syllable (at least, in Donegal). There might be a very few exceptions to this rule, but only in some basic words. I don’t see a problem here. Some other languages always stress the first syllable as well, notably Finnish. If a word is really long, there should be a secondary accent. I don’t think “hiodrainsianna” is particularly long, but the voice synthesis on Abair.ie gives clearly two accents: on the 1st and on the 3rd syllable (and not the 2nd). Well, assuming that the computer synthesis is accurate.
BTW, here is a quote about these flowers from the Finnish Wikipedia. Note that the name of the plant here is actually one of the shortest words! There is always an accent on the first syllable in Finnish, but it’s often accompanied by possibly multiple secondary accents.
Hortensiat (Hydrangea) on Itä-Aasiassa ja Amerikassa luonnonvaraisena kasvava kukkakasvisuku, jossa on 70-75 lajia, joihin kuuluu köynnöksiä ja pieniä pensaita. Niitä kasvatetaan koristekasveina suurten kukintojensa takia. Suurin osa lajeista kasvaa luonnonvaraisina Kiinassa ja Japanissa.