If you want to pay 10 sat/vbyte you should just pay that amount and wait for the transaction to confirm. You won’t get any benefit from waiting for many transactions confirming that pay this rate.
Many services require a transaction to be confirmed within a certain amount of time. This doesn't matter for an online casino, but for an instant exchange or virtually any site that uses a payment processor your unconfirmed deposit shouldn't take weeks.
You are describing situations in which people are effectively selling their coin in fairly small amounts. I don't think tx fees would be a high priority for people in these situations. I think people would care more about the need to buy x, or the rate they are getting.
Also, in my experience, it is more common for sites to require that a tx is 'seen' within a certain amount of time, not confirmed. If you send a tx right after three blocks are found in a short period, and it takes the next two blocks 90 minutes each to be found, paying tx fees consistent with 2-3 block confirmation time will probably still take several hours to confirm.