Long Winded Version - (That's called Inq'ing it)
I kind of feel sorry for the people that created the Arduino. They rocked the world. They created this industry. IoT wouldn't exist without Arduino. I was around before Arduino and it was horrendously expensive and complex to connect say... your desktop computer to Things.
But... they rested on their laurels too long (like IBM). And as China INC is want to do, they will clone you to death. But, sometimes they create something truly inspirational - ESP8266.
I remember when Espressif released it. It was like sipping the ocean through a straw - trying to talk to the world through its AT command set. Then some brilliant, next-level hackers realized they could program it directly. That was a brutal stage for us mere mortals... physically hooking up to it was rough with its non-breadboard-friendly layout and (strange then) 3.3 volts. And the development software layer to program it was like cobbling together a rockets ship using nothing but rocks and sticks.
Then came another brilliant, next-level developer(s) with Igrr, et al https://github.com/igrr leading the way and created the Core ESP8266 that allows us little people to use the Arduino IDE to program it.
On the hardware side, development boards started appearing (WeMos and then NodeMCU) that made all those connectivity headache go away with a simple USB cable to our computers.
There is a rampant amount of information out there that keeps teaching people to use the Arduino with an ESP. Some of it is just old legacy links for those antiquated mid-phases described above. However, the Arduino site https://create.arduino.cc/projecthub/ is filled to the brim with new topics. I suspect most of them are so they can get their project promoted by the Arduino people.
Arduino doesn't make any money unless we buy a real Arduino board. (I'm glad they cleaned out references to the Genuino. All they were doing was confusing new people coming into the field)
In just the last couple of weeks, I counted ten new threads that were using the two units together and were having troubles. No matter how you connect them AT, SPI, I2C, there are just that many more ways to have problems. Especially for a person just getting started.
So... I'm wondering if I'm missing something. Is there a good reason for the mating? My question to you is...
Why do you use an Arduino (real one or clone) in the same project with an ESP8266 / ESP32?
w/ GUI Admin Client, Drag & Drop File Manager, OTA Built-In, Access Point Manager,
Performance Metrics, Web Socket Comms, App API, All running on ESP8266...
Even usable on ESP-01S --- Please check it out!
https://inqonthat.com/inqportal-the-three-line-promise/
https://InqOnThat.com/inqportal