I think that in most readers' opinion, both men benefit equally from the meetings. Morrie needed companionship, but Mitch provided so much more than that for him--he ensured Morrie's legacy, one that is enduring and powerful. Most humans would not ask for more than that.
Similarly, even though Mitch benefits in a very different way from his meetings with Morrie, his "profit" is no more significant than Morrie's. Morrie helps give Mitch purpose and perspective, two elements that most humans spend their lives seeking.
Obviously, Mitch Albom benefited more financially from the meetings because his account of his time with Morrie is a bestseller but also took his writing career in a new direction, one that has proved to be extremely profitable financially for Albom. Who knows if he would have written another book like The Five People You Meet in Heaven if he hadn't first met and written about Morrie?