This is a legitimate question and a suggestion all-in-one:
Wouldn't it make more sense to have a full playset of Lingering Souls over two of your Monastery Mentors?

I personally dont think so. Lingering Souls is an amazing card no doubt, but i dont want to see it more then once a game. Ive tested at 4 copies and at 3 copies and overall i have had the best results at 2 - 3. All i need to do is delay the game until i can resolve a threat. ( Geist of Saint Traft, Tasigur, the Golden Fang , etc... ). After playtesting this list against many competitive decks ( twin, bloom titan, merfolk, abzan, infect, burn); I feel that Monastery Mentor is very underrated in the format. He essentially puts a Monastery Swiftspear whenever you play a non-creature spell and also gets bigger himself. If he is not removed after 1-2 turns , he becomes a huge threat for your opponent. I have also tested him at lower and higher copies but have had best results with 3 .

Thanks for your feedback!

-dylanyad