much of the perceived complexity of Irish spelling comes from the fact that it's changed fairly little from when it first started being written down and it's a language that has been written down for a very long time; but much like say, French, while there are many different ways to write down the same sound, the ways those groups of letters line up to different sounds is itself pretty consistent - a many to one correspondence, essentially, a particular set of letters will usually only be pronounced one way regardless of the surrounding context. Welsh is in many ways even simpler; what to non-speakers may look like a keyroll is actually a very straightforward way to put down its (pretty big!) phonemic inventory as succinctly as possible to the point of approaching Finnish and Polish (another language that gets a bad rep but is actually very easy to pronounce properly just from reading once you know how) in its degree of internal consistency.
compare English where "read" (present tense) and "read" (past tense) are pronounced differently, as are "bow" (the object) and "bow" (the action), not to mention any fucking word that ends in -ough; while even there there's some internal consistency, it ranks up there with Tibetan and Thai spelling as some of the most inscrutable to outsiders out there - all three of which are also languages that have been written down for a long time, evolved quite drastically along the way in such a way that jumbled up the pronunciations of things a lot while the spelling remained largely frozen in place, leading to lots of consonant clusters that simply don't exist in the spoken language ("knight" used to be pronounced /knɪxt/, very close to its Dutch cognate "knecht"). add layers upon layers of loanwords, most adapted little if at all to the way native English words are spelled and you get gestures this mess.
