I would as over the last 3 years
Mantha - 190 GP / 65G / 69A
DeBrusk - 203 GP / 62G / 58A
^DeBrusk isn't far off in numbers and is 2yrs younger than Mantha. Mantha also plays just shy of 18 minutes a night over the last 3 years while DeBrusk has played around 15:30 a night.
Conversely, Mantha doesn't get the amount of secondary assists DeBrusk gets because he is on a worse team and the primary points picture is more in Mantha's favor. He also goes up against tougher competition. He is also right-handed and unlike DeBrusk has shown a clear progressive trend vs just kinda being the same guy for three years with a massive shooting % spike in the middle. And you can't teach 6'5".
Not crapping on DeBrusk at all. He is a very good 1st line/2nd line tweener. Just think that Mantha probably has more value...
BUT, I'm going to argue against myself here after noting that Mantha can walk himself to UFA after taking a 1 year arbitration deal this year which really hurts his trade value.
So you are right, but we just get there in a different way.