While it is true that out of the two functionality will always come up on top of an attractive name, we cannot deny it is better to have both of them.
If you have a good casino but with an uninspired name it would be difficult to promote it, however if you have a good casino and a good name as well that is when you can make even more money as the name of the casino will easily remain in the minds of your potential customers, and they will decide to play at your casino over other similar options due to the fact they remember your casino, while they forgot about other similar casinos which did not left a strong impression on them.
Are there rules that in order to promote a gambling site, you must have a good name first? I believe none but everyone is welcome to get their brands promoted. What only matters there is the money. If you have a lot of money then your gambling site will be promoted almost everywhere and many people will get curious about it and they will start playing.
If you have a good functionality, they can stick to it. That is where you can make more money even if the other one which is the name is not available. Your gambling site will still remain on the players' mind because there is no any other place as that, where they feel contented.
There is nothing written in stone, a casino can promote itself even if they have an incredibly generic name that it will be hardly remembered at all.
However we must remember that a great deal of the money spent by casinos goes to marketing, and to have a memorable name will always be better to have than one that is easily forgotten, as on the first case you can spend less money to promote your brand while in the second you need to spend more money to achieve the same results, and at least at the earliest stages of a casino any dollar you can save makes a difference and it can give more time to the casino to reach success.