I guess it depends on what you mean by genius. I think I would concur with Planxty as being tops in my book, plus each (original) member illustrates a different type of genius.
Andy Irvine is a brilliant musician (mandolin, mandola, bouzouki, guitar, hrudy-gurdy, harmonica, and that’s just what I’ve seen him play), good singer and great interpreter of song, occasional but wonderful songwright, and innovator, bringing a lot of Eastern European influences into Irish music.
Christy Moore is a great interpreter and writer of song.
Liam O’Flynn is one of the best there is on uillean pipes and whistle.
Donal Lunny is a great accompanist, arranger, writer, and producer who has had a far-reaching influence on Irish and other music.
Not only is each of these guys a living legend, they really gelled as a band.
There are others who have excelled in other areas. I think Sharon Shannon has done wonderful things as an innovator who mixes Irish trad with music from other cultures (A traditional Irish reel with a reggae beat and a sax solo? Who else could make that work?).
The Chieftains are a band of great musicians who have marketed themselves wonderfully. I’m not crazy about what they’ve done in the last decade or two, but I do give them credit for bringing the music to a new audience.
Seamus Egan is so good on so many instruments it’s amazing. (Actually, I wish he’d play the flute MUCH more than he has lately.)
Just my rambling, not particularly well-informed and definitely incomplete opinion, Charlie