I bought a Wahoo Elemnt a few month for a simple reason: cycling is for me the most demanding use of the phone, having the phone and cycling GPS separated is better on the long run and allows to choose phones that wouldn't be in the options if cycling is in the requirements.
While it is true that navigation apps have gotten better, cycling GPS have also gotten better. The main gripe I had with my old Garmin unit was to copy routes to the device, which isn't a problem anymore. Current devices synchronise routes automatically with popular apps, display notifications and provide the GPS measurements to the phone for live-tracking features. With navigation, I personally don't need more when riding.
Using the phone for cycling basically requires to take a large phone to have a large battery. Also, cycling causes additional wear on the phone battery: first because of the obvious use of the GPS and the display when riding. And also because direct exposure to sun heats up the phone and then the battery: exposure to heat also increases wear on the battery.
Another concern I have if keeping the phone "as long as possible" is linked to waterproofing. After replacing the screen or the battery, the phone can't be considered fully waterproof anymore. If you don't use the phone mounted on the handle bar, it can be stored in a place less exposed to water (waterproof pocket in a bag).
Regarding the choice of the phone, I prefer small phones, that have by design smaller batteries (that would also wear faster in case of heavy use). Given phones are now mature products, I also don't mind having an older model (I don't like the 'jewel' feeling when having a new phone).
To complete my answer with my 'purchase history': my main phone was an iPhone 7 Plus. After purchasing the Wahoo, I replaced the 7+ by a refurbished iPhone SE 2016 (with a new battery). When using Spotify (and live tracking from the GPS), the battery drain on the phone is about 8-10%/hour, and I can leave it plugged to a powerbank in my bag if needed. While there are some drawbacks (photos — size is for me a trade-off, not a drawback), I retain that the combo 'small phone + cycling GPS' works very well, if you don't need a large phone otherwise.