I booked a trip for Aug 19-24 back in the spring when the crowd calendar had DL listed between 3-6 most days. At the time I didn't know much about how AP holders affect crowds, so imagine my shock when a few weeks ago, most of those days went up to 9s and 10s! Looking back to 2015-16 for the exact same unblocked days, the crowd levels proved accurate between 3-6 depending on the day. I know there's the railroad and riverboats and Fantasmic, but do you really think the parks will be mobbed to 9-10 levels? Or maybe just in the later afternoon?
So there's good potential they will be mobbed as all of those things you mention have been out of play for 18 months. For local Passholders who go weekly that's a long time with those days being some of their earliest opportunity. However, DL is offering $79 block out tickets to that same audience to say goodbye to MSEP which depending on how many Passholders fork over that extra dough could lessen the mob for once the blockout is lifted.
Also, this year's numbers have had much more impact by local Passholders than any year before. Usually tourist season has more to do with crowds, so the traditional first week back as school has usually been a great time to go. This year was also the first year in awhile that they allowed new sales of the SoCal passes (the last little while they have only been available to someone renewing that pass). I don't think it's any small coincidence that all of a sudden when they allow new sales of the pass that the crowd numbers are more heavily impacted by these SoCal pass block outs. So looking at prior years is a little less helpful in that case.
Lastly, DL has announced cutbacks of CM hours/shifts so that also was factored into raising the CL as less CMs mean rides cannot run on full capacity meaning longer waits which is what the CLs are based off of.
Regardless of all the above, with going to the parks at rope drop and having a plan you should be able to still have a boomerang time even with 9-10's and if it does happen to be more on that 6 side then BONUS for you!!!