How many days do you plan on taking to summit? Which route? It sounds like you spend a lot of time in the mountains so I’m guessing you have your kit pretty well dialed in. My summer Rainier kit is slightly different than yours. I think of summer on Rainier from late June to sometime in the beginning of September.
For the slight increase in weight and volume I take a 15* bag. It can still get pretty brutal on Rainier in the summer and you don’t have a lot of layers to add. As a local you can always make the bag choice in the parking lot, but as I'm traveling to get there I take the warmest bag I think I will need. I take a long sleeve white base layer. I like the sun protection and reflectivity. I’ve cooked enough times on a snow field or glacier to always have a white layer available. I think it's more practicle than a t-shirt. I’d add an r1 hoody or something similar. When you head off at 1:00 AM to summit there’s a good chance that it will be sufficiently cold that a base layer and wind shirt will not be enough insulation and I’d rather have the versatility of the r1 for a layering system than dealing with my heavy insulation. I like the driclime wind shirt, but wish it had a hood. I have a wild things hooded wind shirt and I don’t leave home without it, ever. If you had a hooded wind shirt and the weather was clear for heavy rain I’d ditch the anorak. I’d ditch the parka and take a micro puff hooded jacket or the equivalent 100g primaloft jacket or hooded down sweater as my heavy insulation. With the r1 layer in all but the worst summer conditions you should be ok without the parka. You can always have a parka in the trunk of your car and make the decision in the parking lot based on the weather predication. I also like to take an extra pair of gloves, a neoprene half mask and trekking poles. Are you planning on having both a sun and cold weather hat? Light base layer for your legs? Pair of running shorts?
I would wear the nepals because I hate cold feet. With a single boot I’d also have at least one extra sock system.
As much as it would be nice to take the verto, it will be too small unless your climbing partner is taking the rope, your harness, your crampons, some of your water and food. I’ve seen them with a picket and ice axe attached and they look good. It would be a great summit pack. You could probably get it all in/on the prophet, but I’d go for the andinista. Fill them both up with all your gear and figure out which one you’d rather carry.
This is of course what works for me. My partner and I can move reasonably fast up and down the mountain, and I am comfortable with my kit having worked it out over a number of trips.
Enjoy your trip.