One thing I have come to appreciate about WhatsApp is its ability to handle low bandwidth environments better than iMessage. Back in 2015, I was traveling around Europe and had T-Mobile's unlimited roaming plan. I think the data speed was capped at like 64 or 128kbps? In addition, many hostels had less than 1Mbps wifi. iMessage would just choke trying to send pictures or large messages. In particular, it would be stuck in the middle of that "sending" blue line indefinitely like it was quietly timing out and would sometimes require a reboot of the phone to recover because it would remain stuck in the "sending" phase forever. Whatsapp seemed better tested and more solid when it came to transmitting messages. You'd see consistent progressing updates in the progress bar until it either timed out(unlikely) or finally transmitted.
I disagree, this is an anecdote but I ordered a bag of coffee from their "Ship to Store" option. When it came time to go to the store to pick it up, I was waiting about an hour to receive my item. Their setup is very good. You walk into the special "pick up" area of the store, then check in. From there someone is supposed to go to the back and fetch your item. That person was nowhere to be found. After alerting the manager that person eventually showed up and then proceeded to look around for the item. They then decided to call in a colleague who then took even longer to find the item. Turns out it was in a box right in front of them. All in all I wasted an hour trying to get a small bag of coffee. I'm gonna try again because I want this thing to be successful but man was it "nails on chalkboard" experience.