It depends on both players' damage %s. The player with the lower damage % will have greater control.
If your opponent knows he/she also has control, then yeah, it'll be difficult to pull off Bowsercides, but still possible.
Just remember that it isn't always in your best interest to pull off a Bowsercide. If you're in the % lead, it'll be tempting to get an easy one, but it would be a foolish idea unless.....
1. You're both on your last stock and you're confident in your ability to jump out. (or the tourney isn't using the Unity Ruleset and will give the win to you)
2. You have 2-3 stocks to his/her 1.
Otherwise, you're basically helping your opponent. Most of the time, you should just kill your opponent the old-fashioned way. Bowser shouldn't have to resort to killing himself unless he absolutely has to.