Betting 10% of your bankroll on every bet is also unwise, very unwise to me because what this means is that you only have 10 bets or spins (depending on the type of gambling game you are playing) that ends in a consecutive loses to completely end up with an empty bankroll.
Betting this amount of money can maybe be profitable if in a couple of bets or spins, you win an amount that more than doubles of triples your entire bankroll, even at this, you will still have to maintain that particular amount of money you have been spending on eat bet or spin, or you still risk losing your bank easily if you continue to maintain spending 10% on spins or bet and you hit a long losing streak.
I think that this depend on the kind of bet you are talking about. I might want to reduce my number of rounds on some certain games but that's not too big on an average bet. If you are using $100 bankroll as OP stated, I think it's okay to say 10% is a safe bet which is $10 and with 5 odds, that's means you will be getting potential $50 profits which is 1:5 ratio on a 10% of your bankroll. Unless we want to consider this as subjective but it's still the same unless we are considering large amounts of money.
What if we consider huge amount of money with 10%, this might be still be subjective in the sense that betting 10% wouldn't look bad. What we should be talking about should be why someone need to be betting 10% of your bankroll. If you are really good in betting, like an average person with minimal lost, even if you bet more than 10% of your bankroll and you win most often than you lose, I don't think there is really a problem with the 10% allocation for wager or stake.