The ESP chips are not trivial to hook up, unless you get something like a NodeMCU. The original breakouts are not breadboard friendly, and they have (comparatively) weird requirements for programming (e.g. some pins need to be pulled up, which means you need to breakout the breakout boards). They're also not 5V tolerant, which means you normally need a regulator and have to worry about interfacing. The documentation is OK, but it's a warren of official documentation, Wikis, Github and forum posts.

I would say that the Arduino advantage is that it's truly out of the box. ESP8266 is close, but it's not that easy.

If you want an easy IoT dev board, I will always recommend the Particle Photon (no affiliation). It's $20 and has really great documentation. It will do OTA updates out of the box once you've set it up on your network using a smartphone. It's a separate IDE (cloud based, or you can get an offline one), but you still use Wiring and they've retained the setup() / loop() constructs. I have had some issues with devices not connecting to networks using the chip antenna, so you probably need the external one.

Other minor issues - most ESP boards are not FCC/CE compliant. They're just fake stamps on the EM shield. Some of the boards are, but you need to be careful if you're trying to build a product or worry about interference. The Photon, on the other hand, is certified (and they also certified it with a suitable external antenna).