I think you are probably low balling the numbers the steamboat/ TSI do and greatly overestimating the numbers the cars ride will do. 4,000 riders per hour? That isn’t remotely possible.
I'm possibly low balling but the actual capacity that you can look up is 450 guests at 1 time. That is an actual capacity and backed up by similar boats having a similar but slightly higher capacity due to the the lack of theming on those boats. Then the actual ride time for the riverboat is about 20 minutes. Meaning you can get 2 trips in per hour (2.5 or so but I digress)
The Cars ride at Disneyland sees a capacity of around 1,000-1,500 hourly.
I was generous to put in a capacity of 1,000 for this even though our rides capacity would be most likely on the higher end of that due to its shorter size.
Mators Junkyard Jamboree (a ride heavily suspected to be the secondary attraction in the area) has a capacity of approximately 600 per hour.
Villians land is ALSO replacing this area. I calculated Maleficient's ride capacity to be similar to Expedition Everest due to an outdoor themed coaster with show scenes and a single load station platform. That ride can serve a total of 2,000 riders per hour (everything is theoretical)
The other ride people have no real idea about but since a front runner that would be fair is a boat ride, I'm going with a lower capacity boat ride with Frozen Ever After (only 1,000 guests per hour compared to the juggernauts of POC and IASW at 2,000 guests per hour)
1,000 + 600 + 2,000 + 1,000 = 4,600 total RIDE capacity, not counting the new dining and shopping confirmed that would certainly take up capacity. There is no reasonable way that a ride that can't even crank out 900 riders per hour as a MAXIMUM would be able to touch that even with a "quiet and remote" island that people love because its NOT busy. The absolute maximum you can even give the island is a ridiculous 1,000 people per hour which I dont think it touches even during a busy season as that would require every raft (every 5 minutes about) to fully load its 55 people and be operating at peak efficiency.
It's a complete decimation in a numbers game and it isnt even close.