I disagree with them.

1. Emojis do not look the same on all platforms. Let's take white large square ⬜ for example. Emojipedia shows what that emoji looks like on 26 different vendors. Some are pure white, some are shades are grey, and then there's Microsoft who in its usual infinite wisdom decided it should be purple. large yellow square 🟨 is a tossup between actually yellow and orange. This issue is also exacerbated with different displays displaying colours differently. Factors such as color accuracy, viewing angle, brightness affect how you perceive colour.
   

This also extends to face emojis. grinning face with big eyes (Emojipedia link) isn't that easy to tell apart from grinning eyes (Emojipedia link)

2. Emoji support depends on your device. I'm on Windows 11 22H2 which recently added support for shaking face 🫨. Problem is, Windows' emoji picker Win + . (period) doesn't have it. Trying to login on a friends phone that's still on iOS 15 or Android 12, before shaking face came out? Enjoy manually copy/pasting the emoji from Emojipedia.

correct horse battery staple on the other hand looks the same on all devices.