I think it's very hard to card count in black jack these days. Going to a physical casino alone without a team is almost impossible. It is very suspicious if you are standing behind a table and just count the deck for 20 minutes and then suddenly jump on the table at start betting the maximum amount. Security will be pretty much be on top of you within the first hour of gambling and you just end up being banned from the casino. With a group of people - multiple spotter - at least 2 gamblers - 1-2 decoys - and a good exit strategy it might be possible.
The claim that there will be a security is an overstatement and an exaggeration. As if an individual will bankrupt the house by just winning in blackjack, there is a reason why there is a variety in casino games. If you want to practice and you put effort into it, I think you can be good at it and do not treat it like a heist movie where you form an Oceans Eleven squad. If you know what you are doing then you can pull it off alone. I do not believe that casinos will just ban someone because they are winning. They do not care about you winning as long as you are losing in a patterned basis.
I not saying that you will get busted a 100%, but the risks are pretty high in my opinion. Counting cards is banned by casinos and the security staff is trained to spot people exploiting it. Winning on the table doesn't make you suspicious, but standing behind the table and counting the deck is. Also working alone makes it so much harder, because just by counting cards doesn't mean it's a guaranteed win. You can be counting the stack for 30 minutes without it getting it in your favour. That's why there are usually a few spotters working together, screening a lot of tables to find the best one.