It's one of those things where I've been using chrome for so long that switching to anything else is infuriating. Trying to learn the layout and all the features. Trying to figure out how to do things that are intuitively design on Google.
If someone made pretty much a 1 to 1 copy of Google without all the bullshit I'd use it in a heartbeat.
I have the same problem the other way around. When I use chrome it feels like I'm using a kids browser. Slightly cutesy with too many curvy bits. Sort of like the difference between Duplo (chrome) and Lego (Firefox). Basically the same thing, but also not.
UI in Vivaldi is unique, you can set it to simple as an old IE or to an dashboard of an Spaceshuttle and everything in between in the settings and more with CSS. Also using of more than 4000 themes, or made and share your own. You can install Chrome extensions, but most are redundant because of the own inbuild ones, or even install directly userscripts as extensions.
This is certainly a hurdle to overcome. Google helped by changing the Chrome UI for the worse in some ways I care about, but migrating to a new browser and getting used to different UI is enough of a hassle that I'm still holding out until adblock actually stops working before I make the switch.