If he continues his meteoric rise, and in today's market, yes.
Pogba's influence on the pitch is massive, he's rightly regarded as one of the best midfielders in the game right now; and at the age of 23 he's only going to get better. Most midfielders reach the peak of their footballing ability at the age of 27 and in most cases is carries on to their mid-thirties. Pogba is an investment.
Sure, he doesn't score 40 goals a season like Messi and Ronaldo - which I agree should be taken into consideration - however, he has the ability to control a game all the same. The sheer dynamism of his play is enough to turn a game within seconds, be it from his incredible passing range; ability to shoot from outside the box; vision in the final third or his absurd footballing intelligence.
Paul Pogba is a generational talent; and that comes at a price. Transfer costs are increasing at a ridiculous rate and it is most certainly a seller's market. Pogba costs so much because he is only 23 and has the ability to become Manchester United's star player from the moment he arrives. With a strong cast to support him, Pogba could grace Old Trafford for another 15 seasons. He has the ability to lead United not only to the top of the Premier League but to the final of the Champions League as well.
£100m is a small investment for a player who could potentially dominate world football for years to come.