My ex father in law was the head of Psychology for the Veterans Administration where he did amongst other things "Couples Therapy" In truth he was a man who had been married 5 times each marriage lasting 7 years. An observation of his grown childrens behavior shows that one is physically abusive towards women and has been to jail for repeat offenses, one has 5 children each by a different mate, one is gay, one runs an online adult business.
The only other "couples therapist" I've ever met turned out to be in treatment himself for sex addiction. So no I don't believe that "couples therapy'' works. The only way a couple can improve thier relationship is if they want to improve it and actually work at improving it themselves.
If you want advice from someone find a couple that has been married for 50 years and ask them what they did right.