On the price & compensation
If you offer sheet Subban to the term and money he's reportedly asking for, the compensation is a 1st + 3rd.
The question becomes - can you draft a player better than Subban with a 1st and a 3rd? I'm not so sure you can, particularly with the Leafs' history of drafting and developing young players.
On sending him an offer sheet
What's the point?
Surely you only offer sheet a player if you feel there is a chance you can nab him?
PK still has the right to refuse the offer sheet, which is something people forget. Just because you throw in an offer sheet, doesn't mean you are guaranteed the player.
Additionally - if PK is offer sheeted by the Leafs, the Habs have to match. You don't lose your star player and face of the franchise, to your rivals. Nashville matched on Weber, and I'm sure MTL would match Subban.
So question becomes - why offer sheet Subban if there's no chance of it leading to a successful outcome? Seems kind of pointless to me. If anything it only fractures a relationship between 2 newly employed GMs.