Soldato
You've nitpicked without acknowledging that the underlying premise might be correct. My iPhone XS that I paid £1000 for is now worth about £550 - 55%. The Note 9 (as one example) is now £350 down from £599 - 58%, though admittedly you couldn't buy the Note 9 for that price until some time after launch. If I'd paid £1000 for my iPhone XS in August (I didn't, but it happens), it would have fallen in value by 45% in a month.
iPhones do hold their value better when you take best case scenario of full RRP for both devices bought on day of release. Once you factor in carrier and retailer discounts, the gap is much less. In some cases, that gap may not exist.
I am specifically talking about launch day prices. I wouldn’t buy an iPhone mid-way through the cycle.
And the only way to make your figures work is to wait for the Samsung device to come down in price new.
So whilst you may have been enjoying your new iPhone for 12 months and still retain 50% of its value you might have only had your Samsung phone for 6 months to get that same value back. Keep the Samsung for the same 12 months as the iPhone and it has lost even more value.