Dough – leave out raw already-formed cookies for close to an hour while I wait for the oven to be available

This looks to me like the symptoms of too much flour - probably way too much.

Measuring baking ingredients by volume instead of weight is always a crapshoot, although it shouldn't be that far off - my guess is that either the flour was heavily compacted, or perhaps the baker's mind wandered off and she accidentally added an extra cup.

Overmixing (i.e. by using an electric mixer) is a common problem with cookies but the symptom of that is a hard and gritty cookie that doesn't rise - not one that rises too much and has unbaked flour in the center. As far as I know, that can only happen with a huge amount of flour. Obviously, too much flour would also result in a much denser dough.

What you ended up with seems to be more like a quickbread - almost a scone - and there is indeed not an awful lot of difference between the two aside from the ratios and the creaming of butter.

Excess flour probably wouldn't result in a stickier dough, but stickiness is more due to temperature than anything else. If you're finding the dough too sticky to mold then make sure it's thoroughly chilled - that will make it easier to work with.

Preheat while doing other things. That's not a step that should take any effective time.

Don't measure so obsessively. Unless these need to be immaculate cookies, just accept a little variety. Scoop roughly with a spoon, or just your hands, and form into balls with your hands if necessary. If you desperately want precision, you could use a cookie dough scoop. But 56±3g sounds kind of over the top to me. Given that you said this is the main time sink, I'd suggest loosening up a bit.

Are you filling your cookie sheets fully? Do they fill your oven? Following a recipe's instructions to the letter, baking only 9 per sheet, is obviously the wrong thing to do if your cookies or baking sheets aren't the same sizes as those in the recipe. Note also that if you have many cookies per sheet, you can often fit more by tiling in triangles instead of squares.

And finally, reconsider your recipe. I'm sure this one is great, but keep in mind that most standard chocolate chip cookie recipes bake at 350F or 375F, and times more in the 8-12 minute range. If your recipe gives you exactly the cookies you want, and others don't, then stick with it, but if you're unnecessarily sticking to a recipe, try something else.

Edit: one more thought! Chilling the dough is probably important to your recipe, but you could measure/scoop while it's warmer and easier to work with, then chill in balls, and do the final forming once chilled.

And another, having seen your comment: given that you increased the baking time upon filling up the oven more, and are using insulated pans, you might actually want to increase the temperature to 350-375F and see if you can get back down to the 15-18 minute baking time. They may end up closer to the originally-intended consistency!