too much for tavares, he'll sign for less

12.5 gets them two high end defensemen.

Giroux signed 3 x 6.5 . Tavares will do the same but you gotta account for a higher cap

Walk then Mitch.

he got his big pay day already, already started his family there, he'll sign for less dw

Not really, assuming you mean by high-end top 4+, at 12.5M they could maybe get like two Severson's if they are already on the team or acquired via trade. Realistically, they aren't going to be able to acquire two guys via trade unless at least one of them is aging. It could happen via free agency but that would probably cost them 13M-14M+. I could see Marner get like 13M, but at the end of the day it's highly unlikely that they would get the opportunity to spend that money better (meaning they actually improve overall as a team and not just on paper with a more "balanced team).

The type of high-end defender that the Leafs need is another top 2 guy if anything, and that would easily cost them 8M+ (probably 10M+) via free agency if there even is someone available.

I take your point about the exact dollar amount, but I could imagine a pair of players, maybe one at 7 and one at 5.5 that would play above everyone they have now except Mo Daddy. Available is of course its own challenge, since pending UFAs today may get extended before July 1 next year.
I'm sure you've encountered more than one person who does not accept the "just wait 'til next year" playoff potential of this core four occupying almost half the team's cap space.

Well even with retaining Marner, they still have room to bring in one 5M to 7M guy. So really, it would be more about bringing in a forward+defense pair that is making 7M+5M or vice versa unless you're trying to bring in three new top 4 defenders, but I'm sure even if that were to happen there would be a lot of complaints about the top 6. The other thing is that if they do manage to bring in guys via FA, they are more than likely paying more than you want for those guys just like with Marner or Nylander, but instead, you got 2 or 3 guys. The Leafs did have Brodie and Muzzin who at their peak are probably just as good or better than most of the guys that would be available and that wasn't enough to make a difference. The future of the Leafs defense is concerning, but the issue is more a result of the Leafs lack of/inability to draft and develop defenders selected in the 2nd or 3rd round and both Sandin and Liljegren's inability to make a quick impact on the Leafs blueline than "the core 4" too much money. You could maybe say if only Matthews and Marner took less on their first contract then maybe the Leafs could have signed Pietrangelo instead of Brodie.

I think people are getting ahead of themselves. This year isn't over yet, and it might very well be their best opportunity to put together a team to win the cup over the next few years. If they win people won't care too much for the next few years, since they will be optimistic, but if they don't which is highly likely then it's doom and gloom until they win if they ever do. The core 4 currently takes nearly 50% now anyway, so it's just the status quo beyond this year. I get that people aren't happy with that since things have been overall underwhelming thus far, but eventually, they will have more money to spend, the question is will they have a high-quality defender that they can spend that money on?

You again?! I thought I had successfully banished you to the shadow realm what the heck are you doing back here???