Muay thai is great when Incorporated Into a well rounded striking game. and when properly adapted to MMA.
But, It's Important to train boxing separately right from the start. Muay thai gyms teach you far too many bad habits with your hands and those neural pathways can be difficult to change when they're so deeply Ingrained into you.
Traditional martial arts are definitely seeing a resurgence at the moment. The Footwork, movement, stance, wide base, diversity and creativity of attack and defense lends itself well to MMA. Particularly when combined with proper pure boxing training under a respectable coach.
Muay thai isn't at all out of place within the mix. There are many weaknesses as a core striking style, particularly in MMA.. but It has it's place and It would be silly not to incorporate some elements Into your overall game.