I do not think the main character of a thriller always needs to be likeable. The reader does, however, need a reason to stay close to them.
While writing Milan de Winter, I noticed that making him kinder also made him less interesting. He became easier to approve of, but he started to feel less like a real person.
I have chosen to let him make decisions that readers may understand without always supporting them.
He notices more than he says, protects parts of himself and sometimes waits too long before acting.
For me, curiosity matters more than perfection.