To begin with, I don't think anyone, anywhere will ever say the Mitchell trade won't be considered a fantastic trade. I literally have no idea what Sydney were thinking. They traded him for a single teens pick (#14) and a later pick upgrade. There is not a team in the comp who wouldn't have taken Mitchell on those terms. It was completely, totally idiotic, even moreso when you consider Hawthorn had no bargaining power and are a premiership rival. It boggles my mind to this day, and will continue to do so. Even if Mitchell gets hit by a bus next week or pick #14 (Marshall) turns into the next Lloyd/Franklin it was still a terrible trade. Whether or not T. Mitchell is as good as one of Lewis or S. Mitchell is totally besides the point from the POV of if it was a good move, although obviously still totally relevant in considering if their midfield is stronger this year compared to last year.
O'Meara is a different story. The deal was:
OUT: picks #23 (Hill compensation), #36, #48, #66, #70 and their 2017 1st and 2nd rounders
IN: O'Meara and GWS's 2017 2nd rounder
Given GWS is likely to finish top 4 in 2017, the odds are that is a second round pick downgrade, with the extent depending on Hawthorn's position. That is a monster set of compensation for one player who has missed two years with injuries. That is a lot of picks for players that could come good for O'Meara to beat if you're considering his value in the trade. It has totally ripped out any chance of a rebuild via the draft for the next two years as well.