I think people very much overrate late 1st rounders, which is where Toronto's should be. Using recent years (ignoring the very most recent few, as they haven't had time to show results yet):
2010: Howden, Kuznetsov, Visentin, Coyle, Etem, Nelson
2011: Percy, Danault, Namesktnikov, Phillips, Jensen, Rakell
2012: Schmaltz, Gaunce, Samuelsson, Skjei, Matteau, Pearson
2013: McCarron, Theodore, Dano, Klimchuk, Dickinson, Hartman
2014: Pastrnak, Scherbak, Goldobin, Ho-Sang, Kempe, Quenneville
2015: Roslovic, Juulsen, Larsson, Beauvillier, Carlsson, Merkley
2016: Tufte, Thompson, Howden, L. Johansen, Frederic, Steel
2017: Poehling, Oettinger, Frost, Bowers, Jokiharju, Tolvanen, Kostin
Total: 49 picks
Guys clearly better than Rakell: 3 (Kuz, Theodore, Pastrnak)
Guys in similar tier as Rakell: 9 (Danault, Rakell himself, Schmaltz, Kempe, Roslovic, Beauvillier, Frost, Jokiharju, Pearson)
So, late first rounder has roughly 6% chance to be better than Rakell, 18% chance to be similar to Rakell and 76% chance to be much worse than or a bust.
Based on the above, Rakell for a late 1st + B prospect (who probably is equivalent to a 2nd or 3rd rounder), is a pretty bad value (despite being a typical/standard) offer.