I would suggest you both of Brand Name and site functionality as branding is so important these days due to search engines as for instance when u search gambling is faster to get "gambling.com" site rather than other non named such.
Same thing for functionality as the more you have the more appreciation and enthusiasm some new gambler will have to join your gambling site.
As i see the most casinos don`t have "gambling" in their names but have smth about gambling. For example - Stake. Very short and memorial brand name. I think "stake.com" gamblers will remember but not "gamblingwiththebestodds.com " Possible that it will be harder for promotion but i think that you can`t get easy and short "gambling" domain names nowadays, only smth near gambling. Like as Stake.
Complicated names are not suitable for quality branding.
It is better to use short and catchy online casino names. The name of an online casino should be read the same in all major languages of the world. At the same time, it should be perceived pleasantly to the ear (and not as a curse) by all the inhabitants of the planet.
It is important that the name of the online casino evokes positive associations (reliability, success, wealth, winnings, profit, luck).
It makes sense to involve professional marketers in branding. You may also need legal advice (because some titles are subject to legal protection).