Alpine starts and lack of sleep are just part of the inherent stress that needs to be overcome to climb mountains. I think you might be putting too much blame on the lack of sleep and not enough on the lack of fitness. Rainier is not an easy mountain. If you had been fitter the effects of the lack of sleep would’ve been the same relative hindrance but you would’ve still been able to perform at a satisfactory level to keep slogging.
If I have to drastically shift my sleep schedule I take melatonin. It allows me to fall asleep much earlier than I usually would, thus getting enough sleep so that my day just starts super early on the alpine start. If you know in advance that you’ll need to get alpine starts (say you’ve got days scheduled on rainier), shifting your sleep schedule to going to bed super early could completely solve the issue.
I’ve also had pushes where I’d drive from revelstoke on a friday evening, get a nap at the columbia icefields parking lot and start climbing in the middle of the night. I don’t habitually drink coffee, if I’m doing something like that I’ll have tea with my breakfast. Caffeine is an extremely effective stimulant when you’re not addicted to it. I find I can move for about 12 hours before the lack of sleep really starts catching up to me, with enough fitness for a properly planned objective it’s enough for me to be out of the way of objective hazard (I wouldn’t want to be there mid afternoon anyway) and able to catch a nap back at the parking lot or in an island of safety. I’ll usually squeeze a few minutes of shut eyes if I hit a warm spot with no overhead hazard on a summit ridge or a col or whatever, and then get a couple hours nap at the car after climbing before safely driving back into town.
I have experience with forcing myself to stay awake through my late teens’ party years. I wouldn’t recommend skipping sleep on purpose, it’s just unhealthy. However I do think there is value in experiencing how your body responds to lack of sleep and learning how far you can push through, as well as what happens when you sit down completely exhausted and just fall asleep no matter how much you’re trying not to. With more alpine starts and long pushes you will become familiar with how your body reacts to being tired, and you will learn how to deal with it.
I’m glad you asked the question. I’m sharing my experience and thoughts here and hoping it’ll be of use to you, but I will be really happy to read other climbers’ insights on the matter. If I can piggyback on your thread, I’d love to hear if there’s anything that can be done with regards to recovering after skipping sleep due to getting an alpine start.