Everyone has been really critical on Drouin over the years, including myself; so much potential, but never lived up to expectations. When he's on, he shows how talented and dominant of a player he can be. Flashes of the first line winger everyone was hoping to see. Too bad that it only lasts for a dozen games or so; he did show promise in his first dozen games this year but then got injured and did not look the same after.
Anyways, despite all the frustrations, I personally wouldn't trade him for an 18th overall 1st round pick. As inconsistent and disappointing as he can be, he's an established talented NHL player. Even at his worst and in an inconsistent bad year, he can still easily hit 50 points which is pretty good for your average top 6 winger. There's a huge misconception around how a 2nd line winger should provide around 25 goals and 55 points. Truth is the average contribution of all the teams' 2nd line forwards is way below 50 points.
As for draft picks, they do look sexy and people like them here on this board, myself included (after all, we are on HockeysFuture). However, every year, even in the most promising draft years with high quality prospect pools, you will see a fair amount of 1st rounders flop. Some will never make it to the NHL, others won't even come close to becoming the player they were projecting to be. Obviously, players picked top 5 overall and those in the 6 to 15 range, have a higher probably of making the NHL. Those picked in the 16-31 range will unfortunately have a lower probably of making it. Statistics show that in average, only about 65% of those picked in the 16-31 range make it to the NHL, without taking into account what kind of player they become (the 65% even include those who manage to play 100 NHL games, but never have any impact and continue their careers in oversea leagues).
That said, a 1st round player picked in the 16-31 range turning out to be a Jonathan Drouin would already be considered a successful pick (not great, but not bad either). Sure, you may hit a homerun with a player better than Drouin every now and then, but probability is not that high and there's certainly no guarantee. There are also good chances that the 18th overall pick never amounts to anything.
Now back to the Canadiens, a team desperately in need of goal scoring and more offensively talented forwards, Drouin is still a valuable asset. He's been a huge disappointment because of how highly touted he was when he was drafted; people were expecting him to become an impact player like Nathan MacKinnon did. He's also hated by a lot of fans because of his pouting history with the Lightnings and what the Habs gave up to acquire him (the almighty 9th overall 1st round pick Mikhail Sergachev). If we remove our biased high expectations and hating lenses, he's actually already a decent skilled top 6 winger. He's not a driving force but a good complimentary winger, capable of producing on a top line with talented players. Drouin will not look good playing with players favoring a dump and chase grinding game (unfortunately the style of most other forwards in Montreal). He'll produce playing with players favoring a strong puck possession game (that's why it looked like he was finally clicking with someone during the playoffs; Suzuki is probably the most talented puck possession player he has played with since joining Montreal). Drouin excels at give and gos, using his speed, maneuvering with the puck, passing it back and forth etc. I'm now curious to see how Drouin does playing a full year with a player like Suzuki (their game seem to compliment each other well).
I don't think at this point, anyone expects Drouin to become a dominant force. There's still hope however for him to become a more consistent offensive top line forward. Let's not forget that Drouin is just 25 years old and entering his prime years; his best days might still be ahead of him. Worst case, he stays the inconsistent 2nd line winger he already is and the sad reality is that he would still be one of Montreal's most gifted player offensively.