I find it mostly depends on your personal motivation. If you somehow are magically motivated to slog through a huge amount of crap that seems meaningless and pointless to everyone else, bottom up is preferable. You'll end up in a better place in the end. But... it only works because you see the meaning and point of investing a large effort before the tangible payoff. Bonus points if you find the slog to be fun in and of itself.

Naturally, a lot of professors and highly talented experts tout this as the only way to go. It worked great for them and they don't see the point of any other path.

But, in my observation, "talent" is usually a false explanation of someone who is highly motivated by something I'm not aware of. Most "talented" people I've known were actually putting in a huge amount of work in the area.

On the other end... if the return on investment isn't clear. If the path to the payoff is branchy, windy and foggy. If you are motivated by results, not process. Top down is a good way to determine if it really is worth the effort. In the meantime, investing some extra effort in finding the payoff and the joy in the process would be wise when taking this approach.