Well, of course at a certain point size, strength, and surprise will play a role. A 100 lb woman is not going to control a 300 lb NFL lineman with a wrist lock.
If the two people are relatively close in size and strength though, then they can be very effective if done correctly. The ways that I was taught to utilize them, which is honestly slightly different than how I see them usually taught, were developed from working with incredibly strong and powerful people.
The element of surprise is also a crucial aspect. If I tell someone who is bigger and stronger than me that I am going to wrist lock them and to resist me fully, of course it’s not going to work. On the other hand if it comes as a complete surprise to them my chances go up significantly.
And finally, no technique works 100% of the time, so you must be able to flow to other skills, or escalate to greater levels of force should the need arise.