@wonghow: There was no feature to save tab groups in Chrome initially. Just because Opera added a single extra feature of automatic tab grouping through links doesn't mean it's any different. Besides, in Opera, you can Ctrl+click to select tabs and create tab islands of tabs that aren't even related by links! So, it's Tab Islands are just like tab groups but worse. Grouping tabs by links is a feature that already existed in many Chrome extensions before Opera even released Tab Islands. I don't understand why you insist that they are fundamentally different. They aren't. Tab Islands is just a bad implementation of the original tab groups in Chrome.
Besides, having a feature where you can name tab islands wouldn't hurt. You will still be able to have unnamed tab islands just like unnamed tab groups in Chrome.
At the fundamental level, Opera tab islands use the same concept as Chrome tab groups; it just adds a functionality of auto grouping by links while discarding other functionalities of group naming and saving groups. If the base code for Tab Islands and Tab groups weren't the same, then the same chromium tab group extensions wouldn't work in both Opera and Chrome, which they do!