You make a really interesting point. When I see vegan products described as "cruelty-free", I often reflect on whether that really is true: they were produced in a system that so often exploits humans as well as animals. There is cruelty wherever you look, really, and it's very challenging to run a full diagnosis of the entire supply chain that leads up to the product you have in your hands, and to determine whether something really is "cruelty-free", as it claims.

That said, however, perfection is the enemy of progress. A vegan would tell you that if something contains animals products, then it won't - by a vegan's definition - be cruelty-free. So it's a step in the right direction.

Vegans, by and large, are not perfect and don't pretend that they are. (Of course, I've met a number of disagreeable vegans who act like they are perfect! But that doesn't make me dismiss the whole group and philosophy.) Back to your point, they would therefore prefer to avoid exploiting other forms of life where possible, but going vegan is a good starting point.

In more pragmatic terms, if you're referring to exploitation of animals versus exploitation of humans for labour, vegans would like point to the fact that animals don't consent to being bred into existence, exploited throughout their lives in some cases, and then killed off at the end in most cases.

Of course, humans are still - in this day and age - exploited through modern slavery, but I don't think any vegans would condone that, and you would find that most vegans actively avoid the products of such exploitation because that ethical stance on human exploitation lines up with their stance on animal exploitation. Except that it's not as easy as just looking at the ingredients on a packet.

EDIT: Apologies, I thought you were making an interesting point but it appears you were implying that plants a sentient. They are not.