If SoftSwiss is really trusted data source, then the data could be accurate because am not even surprise that Bitcoin is the most popularly used coin on the online casino, perhaps which only casino that doesn't add Bitcoin as part of their ctypto? I have not seen any casino that doesn't use Bitcoin and as we know, Bitcoin is a universal coin and casino too trust the solidity of the coin which is why they will mostly use it.

Tether is kind of a no-brainer, but with Litecoin and Dogecoin I assume it's mostly because they've been around quite a bit longer than Solana and Tron. So older Casinos will offer them even if they haven't added new currencies for a while and newer Casinos will offer them because the older ones do. And in the end users will use whatever currencies are made available to them.

For the first two cryptocurrencies it's anticipated that they should occupy the first and second position from any other source that the report may be coming from, but what's weird in my opinion is seeing litecoin designated 3rd over tether seem kinda weird cause I thought a lot of gamblers would be using tether for betting than they do with any coin after BTC and Eth. Perhaps litecoin made it into that position over tether base on transactional usage due to its low fee over tether.

Except Tether, other coins in the list are mostly Proof of Work, and Ethereum was a Proof of Work altcoin before it changed to staking.

Proof of Work coins can not be created from thin air like Tether or Smart contract altcoins and PoW coins are more safer choices for users and companies. Less risk of rugpull than with Smart contract cryptocurrencies.

New altcoin blockchains like Solana and Tron need market tests, security tests, hack tests practically before their blockchains can become stronger and attractive for people to use and companies to deploy on their platforms.

Ethereum used to be in this comparative table when it was PoW.
https://howmanyconfs.com/

I wonder what stats did they collect.

Are they collect the stats in terms of cryptocurrency used by each account or the total volume? if it the first one, I agree Bitcoin is the popular crypto in gambling because people are curious to use other coins to gamble, since Bitcoin is the biggest cryptocurrency, people might curious to use it.

But, if it's about total volume, I think Bitcoin isn't the number one because people tend to choose cheaper cryptocurrency. Even though Bitcoin fees is already cheap, but many casinos charge a lot additional fees.

Not to mention many gamblers said gambling with Bitcoin aren't their choice because if they spent $100 today, it might worth $500 in the next 4 years.

Bitcoin is always at the top and will remain so. I notice the high use of LTC for crypto casinos during the time of when Bitcoin fees were at their ATH. For Tron, I don't know, but I have also noticed that many people even prefer to use Shiba over Tron these days in terms of deposits and withdrawals for the casinos that allow it. I'm not surprise with the coins on that list was not even expecting solana over their instead Shiba is another meme coin I know people often use for deposit too after dogecoin.

I don't think we need any revaluation before accepting the fact that Bitcoin remains the high used cryptocurrency in whatever platform, and we have to accept the fact that gambling most especially the cryptocurrency gambling industry has been one of the biggest supporters of Bitcoin and other cryptocurrencies, so yeah Bitcoin will always rank as highest used, if not some few times when transactions fees could be crazy on Bitcoin network I don't think anyone will consider using other coins to gamble aside Bitcoin, so the ratio of the other coins as just in the proportion of it alternative use when Bitcoin goes high in fees.

I'd be surprise if it is among the list.  Doge somehow I think is created to be just like Bitcoin that can be use to bet on casinos. The old timers in crypto does have millions of it just being wagered in yobit dice for like 50,000 doge every dice roll. One of the oldest casinos in crypto I think have started adding dogecoin even before its price turned $0.001

BTC is not surprising. People think Bitcoin was only created for geek's casino.   

It's probably most of us are Bitcoin hodlers that's why we still prefer it over USDT or any other stable coins. And I'm under the impression that most gamblers still uses Bitcoin today as the fees are no longer a factor unlike last year when it goes very expensive and then we look for other options. I haven't used Solana or Doge, so not sure how quick it is. So the one that I used is Bitcoin and then USDT, obviously the latter as you might want to used it for slot and put the currency to a minimum like $0.1-$0.2. And I think this trend might continue as Bitcoin could still be the widely used crypto by most of us in the next couple of years.