Being pushed into a different tax bracket is something people should always keep in mind. Different tax brackets affects the calculus of which 401k to use (post/pre tax), decisions about liquidating tax deferred assets, it goes on
Moving up a bracket doesn't change all the previous brackets, it just affects money past that level. It's not like a hard line that you cross and it changes the whole picture.
If you think otherwise, give us a scenario where is matters.
Scenario 2: If you want to funnel as much money as possible into your employer's plan, you might want to use a Roth vehicle to do that. (Your pre-payment of taxes on it means that $100 in a Roth is worth more than $100 in a pre-tax vehicle.) Your 401k plan might not support mega backdoor 401k contributions (many plans don't allow after-tax contributions [distinct from Roth]) and you might have other IRAs that would drag in the pro-rata rule for backdoor IRA contributions.