So if I'm understanding this correctly then the Marxist theory goes that human excess population can only be measured by the level of unemployment within society?

Things such as environmental destruction, lack of food and water, species loss, habitat loss, rising sea levels, pollution and climate change are not measures by which we can assess whether the human population of Earth is excessive and unsustainable?

Or at least, if those are acceptable measures of over-population, it's only because they are side-effects of poverty through lack of employment rather than excessive consumption, excessive capitalism or excessive demands on a finite system?