The way it has worked out for me it the iPad stays in the house and the iPhone goes with me when I am out and about. I have an AWU2 and without a iPhone I am missing part of boths functionality if not paired.
While it does NOT seem to be well known and some even deny it's possible (but it's oh so easy to test and see for yourself with an iPad
already on hand), a cellular Mini can easily stand in for iPhone because telephony is just an app... just like Maps is just an app, flashlight is just an app, video camera, music jukebox, tape measure, etc. If one can "think different" in terms of form factor, the actual service of telephony easily disconnects from a brick-shaped computer in a pocket. In fact, install a VOIP app on your Mac and IT can be phone.
I owned an old iPhone for a few days years ago so I could transfer a long-term landline into a mobile number. And since- starting with iPad mini 2 and now 6- iPad mini (with VOIP app + buds) has
doubled as my phone... or- in your wording: it is my "core" tech device.
Besides
costing much less than an iPhone itself, it doesn't "long in tooth" in only 2 or 3 years and 5G data offerings for it tend to deliver a
much cheaper alternative to even discount MVNO phone plans. For example, I average no more than $25/year for 5G service. Yes, that's
YEAR.
Are there some compromises? Yes. But that's to be expected with saving several thousand dollars over life of device. On the other hand, I could easily argue that ALL apps are better with more screen R.E... which tends to be a big reason that many iPhone buyers also buy an iPad.
There are a handful of Apple offerings that have complete dependency on owning an iPhone... but I don't care enough about those things to pay a few thousand more over life of device.
Since you are considering a Mini vs. an iPhone, one OTHER idea is let the former potentially double as the latter. Since you already have an iPad, you can even try this out by installing one of many free VOIP apps on it and just giving it a try for a while. Most VOIP apps will give you a free number (and your number can be ported if you decide you like it). Call yourself and call yourself back. Text yourself and reply to yourself. Use VOIP voice mail. Etc. And/Or involve a friend and learn that your call sounds just as good as making the same call on a "phone." If the iPad you have is not cellular, VOIP apps work great in a wifi zone. Test as is and then- if you want to go this way- seriously consider the extra for cellular so you can connect to the very same 5G as phones.
If you want more on this use, just ask. But I can confirm for certain that- with some compromises- an iPad mini can stand in just fine as a phone too... much like a phone can stand in for a Map or a flash light. I've been doing this for more than a decade now and don't really feel like I'm missing a thing.