I understand the mid-tier players, and even the star, but not super-star, players going after money first and foremost. They have very short careers, and want to set their grandchildren up, let alone their kids. Go after that money man!
The generational players are completely different. What do people talk about when they talk about Dionne, Iginla, or Sundin? They talk about how they didn't win a cup. These are all first ballot hall of fame players, and yet the lack of cups hangs around their head. Hell, look at how Ovi was talked about until he finally won. We are talking about the greatest goal scorer in HISTORY, and the biggest talking point was the fact he hadn't won a cup. If McDavid cares about his legacy, he will sign a very friendly deal for his next contract. The fact that his family line is set for money for generations already, even if he never makes another single dollar, should play heavily into his thinking.
Seriously, stop and think about this. Even if he signed a CRAZY team friendly deal at like $2M/season x 8 years, his career earnings would still be around ~$225M by the time he retires. Even with 50% tax, that is ~$112M USD, or about $150M CAD after tax. That is already generational wealth.
Honestly, if I was in his shoes I would sign a 2-3 year deal at league minimum to try and have a 2-3 year window where my team had a really good chance of winning the cup. He would be 30-31 when that contract ended, and he could sign another large multi-year deal afterwards, and still end up making ~$250-275M in career earnings. I'm not kidding either, money doesn't matter at the end of the day, once you have that kind of wealth already. What you do in life is what matters, your legacy is what matters. Again, I am in my late 40s though, and am old enough to have started thinking about what really matters in life and what I want to be proud of when the end comes. I don't expect somebody in his late 20s to understand this line of thinking nearly as much.