How many deck using on "CASINO" most of live-casino like "Vegas" using 6 deck and online casino probably using 8 deck. In-livecasino you have a many time for make a decision meanwhile in online-casino we have limited time decision around (10-15 second).
Are you sure can counting the card with many deck ( + limited time ? In-online casino you're not gonna to get back off by casino, because is online the question is can you counting the card in online or not ?
And if to this we add that the dealer will shuffle all of those decks more frequently then it becomes way more difficult to use card counting to try to get an advantage over the casino, and even if you could sooner or later you are going to be banned because this goes against the policies of almost every casino in which I have ever played.