Will it actually last 4-5 years if you charge as you like?
Well, in my experience yes. I’ve owned 1 or more each of the original iphone, iphone 3g, iphone 4, 4S, 5, Etc. all the way up to the 11 pro max, and now 13 pro max. Each time i get a new phone, i give my old one to a family member, who then gives hers to another family member, etc. Most times that means the phone is in use for 4 years, but we’ve had a few occasions of 5 or 6. Only one has needed a battery replacement (which, by the way, is not particularly expensive around here for a 4+ year old iphone), and that was after 4 years. I have a shoebox full of old iphones dating back to the original, all of which have working batteries.
And none of us has ever paid any attention to charging. We plug it in each night, sit it on a qi charger at work, plug it in when driving, etc., and it is what it is. When we have long days out and about, it discharges until it goes into low power mode, and, once in awhile, runs out of juice. Just normal usage without any thought about 20% or 80%.
Now, if you run it from 100% to 0% every day, then, yes, you’ll go through full charge cycles every day, and then apple tells you that will degrade the battery if you do it 500 times. So heavy users may want to take different action if they don’t want to replace their battery at some point.