It's not true, as has been shown in the past in other games which have tried this. Other games have ramped up the difficulty, with that mindset that by doing so it'll motivate players to get better.... and all they ended up doing was chasing players away.
Classic recent example was Guild Wars to and the lead up to, and the launch of it's 1st expansion. It's Living World (MSQ) content leading up to the expansion got harder as it was introduced, and there were increasing complaints from players over this. However these complaints were drowned out by the small, but extreme vocal, minority of players who were urging ANet to go harder. Then the expansion hit... and it ramped up the difficulty even more than before.
The result? ANet suffered their greatest ever, or since, 6-month loss in revenue as the majority of their player base abandoned the game... the players did NOT get motivated to get better, to better use skills, etc and overcome the increased challenges. The players hit the brick wall of increased difficulty and left the game. It was so bad that for the 1st time there were threads on both the official forums and GW2 reddit asking where players were... ppl were trying to do content in the either the expansion or the base game and seeing nobody around. ANet had to do a hard 180&, nerf the hell out of the expansion... to stop the players leaving, and their whole studio being shut down by NCSoft (as NCSoft is known to do if/when studio's stop being profitable enough).
Fact is most of the players who would be effected negatively by making the MSQ harder won't 'try harder' or 'play better'... they will take their limited time and money elsewhere. Most of these ppl just want to log in, relax and do the story after a day/week at work... they don't want to be stressed out with a game, challenged or have to watch youtube video guides on how to beat a MSQ dungeon/trial... and if they can't just mash their way through a fight and thus get stuck, they will leave and go play somethign else that doesn't force them to struggle.