Self defense and sparring

Suppose you want to learn martial arts because you want to be able to protect yourself if you end up in a self defense situation… should part of your training involve working with actively resisting partners?
Yes.
Some folks will disagree, but I think if you want what you are training to have a better chance of working, it is necessary to test it under duress. Imagine you have two soccer teams, team A and team B. Both teams have 1 hour practice times 2 times a week for 6 months. At the end of the 6 months, they play a game of soccer.
Now, if you didn’t know anything else about the two teams, you’d probably say the odds are 50/50 that either team could win.
Consider the following scenario. Team A spends 30 minutes doing solo drills every practice and then 30 minutes scrimmaging. Team B spends 1 hour doing solo drills. By solo drills I mean the players are practicing ball handling, shooting, and whatever other things soccer players can do by themselves.
Now, given no other information, who do you think is more likely to win? I’d put my money on team A. There’s no guarantee they’d win, but it seems more likely, especially if we add in constraints like both teams being the same age, size, and athletic ability.
While the example is not a perfect fit, the point is this: if you learn a skill in isolation without the stress of someone actively trying to oppose you, the skill is more likely to breakdown under stress.
What do you think? Is sparring helpful or detrimental to functional self defense?