Not always in the case of sports betting - although there are definitely math "taxes" like parlays and point buys and heavy chalk. Plus all the predatory "promotion" stuff they will throw out. Sharp bettors do exist though, and do make quite a bit of money. They're less than 1% though.
With all due respect, absolutely not? If a book puts out a line of +200 and you've determined there is a certain percentage chance of winning, your expectation easily can be positive. The "gambling is a tax for those bad at math" is a misconstrued quote that usually applies to completely negative expectation games, such as scratcher tickets, in which the more you play you will always lose in the long run. There are very precise mathematical terms for these things, and strictly, you are wrong.
You can extend this to things like poker as well - is that a tax on people bad at math? Of course not, that'd be a stupid argument, because it's not a purely negative expectation game.
