Given the odds are x4.20 and x3.00:
Here’s my simple math.. if you bet $50 at x4.20, your total return is $210.
If you bet $50 at x3.00, your return is $150.
If you take the outside bet (even money), you bet $100 and your return is $200.
So, betting on the moneyline in sportsbook is actually less risky and more profitable.
Apart from the profit, betting on less risky option is really so important in sports betting because the bettor have a high chance of winning their bets than taking so much risk for a high odd. Your math was right and if the OP is still presented with such choice in the future, he knows the best option to take now.