Unless I'm missing it, you are not considering the timing of those deals, the total cap, or other players in our core under contract.
The max cap hit per player is 20% of the cap. Right now the cap is $82.5M.
Using your numbers, the cap would rise to $95.5M the summer McDavid is due and $91.5M the summer that Draisaitl is due, and $83.5 the summer Matthews is up.
So Matthews signs for max, at $16.7M. The next summer, Draisaitl signs for $15M and then McDavid goes to $18M.
That's a total of $33M on a $95.5M cap.... or 34.6% of the cap. That's a lot... but then consider:
1) McDavid only signed for 16.67% of the cap when he signed, and Draisaitl only signed for 11.3% when he signed. McDavid's deal was using Crosby's first big deal... 17.3%. Crosby's second big deal was 14.5%
If we use Crosby's 14.5% (since that's how these things are negotiated), that means McDavid signs for $13.8M and Draisaitl signs for $13.27M. Now we are looking at only 28.3% of the cap, which is pretty much where they were 2-3 years ago.
2) But even if we assume your numbers, let's look at the core. McDrai sign for a total of $33M. Nurse is still $9.25M, Hyman is still $5.5M, Nuge is $5.125M, and Kane is $5.125M. That totals $58M or 60.7% of the cap. We would have $37.5M left for 16 players on a 22 person roster. It's not ideal, but it's doable.
Right now those same guys are making 56% of the cap, 60.7% doesn't represent a huge increase and the cap would continue to rise. It can be held together.
Kane is actually off the books when McDavids new contract would Kick in, but Campbell is in his last year so pretty much makes that a wash. Currently on the books for the 26/27 season is 24,875,000. still needing 17 players plus 1 goalie, but assuming McDavid and Drai are both signed its 15 + 1 goalie. I also think it is a pretty reasonable assumption that there will be a few more contracts on the books between now and then between 3-8 mil)
Lets assume for now;
1) Bouchard 5 Mil
2) Broberg 5 Mil
3) Holloway 6 Mil
4) McLeod 3 Mil
5) Skinner 5 Mil
That's another 24 mil making it 48,875,000 + 33,000,000 for McDavid and Drai that is 81,875,000 still needing 10 players for the remaining 13.6 Mil. Obviously I have no idea how some of the above players are going to project, or continue to play before signing their next contracts, So my guesses could be off 2-3 Mil either way. Keeping in mind that as the cap goes up they would all want a bigger piece of the pie as well. I think at least one of those contracts if not 2 will be in the 7mil range.
Players can also be moved, but I think it is a reasonable assumption that if the Oilers are trying to win for the next 3 years, they will have at least 5 players around the contracts I assumed signed over that period.
It is doable, but if the GM, whoever that maybe at the time, doesn't believe that McDavid or Drai are going to take a discount to stay, they need to consider moving Drai instead of letting him walk for nothing, or cap strapping the team so they are unable to contend.
My belief is if McDavid hasn't won by the time his contract is up, or at least been to the finals, He is going to question if the organization can build a winning team around him. If he decides they can't I think he walks.
If he decides they can, he then decides how big of a discount he needs to take in order to make it happen. He isn't going to take a discount if he doesn't think it changes management's ability to build a true contender around him.