You control weight primary by food intake.
Consider: a person at my height/weight burns approximately 2500 calories/day just by resting metabolic rate. According to this calculator[1], a person of my weight running a mile at an 8 minute pace burns 136 calories. In other words, running a 5k every day would only increase my calories burned by 17%. And running 8 minute miles is one of the more efficient ways to burn calories--if you're doing some other exercise, your calories burned are likely much lower.
Compare the effort involved in running a 5k with drinking two less cans of cola (about equivalent in calories) and you'll quickly see how diet has a much larger effect on weight loss than exercise. There's a reason they say abs are made in the kitchen not in the gym.
[1] https://www.runnersworld.com/training/a20801301/calories-bur...
Working 8+ hours in a manual labour job on the other hand, will greatly increase the calories burned. If people who are stuck at home now don't change their usual eating habits, they will see some weight gains.
Folks who exercise for aerobic reasons, you know, 20 minutes of brisk walking around the park, are getting benefits. But not weight-loss benefits. There's a 10:1 difference in possible exercise regimines. It all depends where you're at in that spectrum. Broad generalities are useless.
You're literally talking about exercising for 1-5 hours depending on pace.
Perhaps broad generalities are useless, but in the context of talking about weight loss, I don't think it's unreasonable to assume that the average person embarking on a weight loss journey is going to jump in and start doing 50 mile bike rides.
It's much more likely that they'll be doing something like a 10 mile bike ride, at a much slower pace, in which case the numbers are back into a range where diet is going to play a much larger role in their success or failure.