It must have both.
Without a reputable name, the casino can't be trusted, and without the good functionality of the website/application, it can't provide players with an enjoyable experience which will eventually lead to the loss of players.
Hopw can you have a reputable name if you're just starting your business?
OP said that many casinos here don't have a good brand name. What does it mean? They aren't trusted? The name of the casino is generic? You have to start somewhere, you can't have reputation right away and I believe most casinos here are reputable, especially those that run signature campaigns for a while.
You can see that a casino is doing well and has money if they can afford to advertise. At the same time a casino that scams will not be allowed to advertise here without serious backlash like negative trust.
Functionality is more important, but I don't see any problems with currently available casino brands
Not all advertise by signature campaign are good and we shouldn't make this as a basis because 1xbit still running their campaign and they had bad reputation here so. We need those both functionality and brand new to determine if they will became reputable or not. Maybe to avoid scam casino best to follow them here and also play only on old time casino because from there we can minimize the risk of getting scam.