1) Marner's potential ceiling is quite a bit higher than Tavares
2) Marner is cost controlled ELC, meaning they can spend salary elsewhere
1) The key word is
potential. Potential is not > what Tavares is guaranteed to provide immediately. Marner is no guarantee to be a superstar. Possible? Sure. Guaranteed? No. Holy hell, HF overrates potential so incredibly. Prospects are not superstars.
2) Good point and does mean something for Toronto right now. Not for long though. If Marner is what you think he already is deserving of being anointed, then hes going to cost sooner rather than later. Tavares is at 5.5 for 2 more, which is a small price to pay for one of the best players in the game right now and will be worth his raise in 2 years.
Tavares is a cornerstone player in the league that you can build around and has arguably not even entered his prime years or is just entering them now and pays immediate dividends espc with what Toronto has already done. There are very few players in the league that you dont trade for him and the ones that you dont are equal/close in age and what they've already been (Toews, Kane, Crosby etc.) Marner is not one of those guys yet. Arguably the only under 20 guy that doesnt get traded for Tavares is McDavid.
I respect your personal opinion, but no NHL GM turns down Tavares for Marner, and certainly not Lou Lamoriello. Lou takes that and runs with it.