Thinking that SWGE is going to only affect DHS is very naive imho
Think of traffic, people coming in and out of DHS. This is why Disney has spent years and millions of dollars in improving, widening and making new roads in and around DHS. This is why the parking lot at DHS has doubled in size, this is why they spent all that money on the skyliner
Now not everyone can afford Disney resorts so they will have vehicles or take buses, ubers, this uptick in cars will affect the roads all around WDW coming in and getting out
People not going to DHS will be impacted by this in a direct way. Those not ready will probably miss fps, dinning reservations
Now lets move to people going to DHS without any or very limited understanding of SWGE, they will arrive at the park, see that's it's virtually impossible to get into SWGE, go to other areas of the park (the smallest park on property) those rides will be filled with people that wanted to go into SwGE and couldn't and people who didn't want to go to SWGE at all.
Most people that visit WDW for multiple days get park hoppers. What do you think they will do when standby lines for all attractions at DHS are very long (think about it, SDD, AS2 still fairly new and getting plenty of traffic, MMRR will be new getting tons of traffic) they are going to move to the other parks. So yes the other parks might be manageable for the morning time but by 3pm they will all be busy. Add to that
MNSSHP and
MVMCP at MK limiting hours at MK
Sure there are different levels of crowds tolerance, but to think it won't be that busy is not the right way to approach this. Plan for over crowding and you will be prepared at worst or pleased at best
So we are not trying to scare anyone, I would like people to be prepared for the worst crowds you've seen and plan accordingly and you can still have a fun visit