Nope, sorry but words have actual meanings and definitions. Slavery is when a person is owned as property. Slavery still exists in the U.S. for prisoners, for example, where the U.S. Constitution explicitly carves out an exception. Now, I don't disagree with your assessment that people on H1Bs have less agency, autonomy, and rights than natives.

But you dilute the meaning of the term 'slavery' when you apply it to someone who has a 100% legally protected right to leave their place of employment and country at any time, without having to pay anything but the cost of a ticket. If an H1B employer holds a worker's passport and makes them work in slavery-like conditions, then that's illegal. If an employer treats an H1B like an indentured servant and makes them pay off the cost of their hiring and immigration, then that's illegal. It does happen in the US, which is bad. It happens far more often to immigrants in places like Dubai, whose conditions often are slavery.

Slavery is really fucking terrible. There is a reason we react so strongly against it. By saying H1B === slavery, you're being intellectually dishonest or using black-and-white thinking.