I think having a contract that depends on the number of hours you spend everyday is a terrible idea. Employee tracking software are the very embodiment of distrust in one's employees or hired contractors. Funny that during the discussion the very creator of such a software is advocating on "trust". I would seriously consider calling such a person out on what seems to be an obvious cognitive dissonance on their part.
Secondly, if a person has any kind of wealth creation ambition or similar such lofty goals, then directly exchanging one's time for money is very poor way of going about it. The person is far better off quoting their prices on the basis of deliverables within some reasonable, mutually agreed timeframe.
Before I started working full-time with my current organization, I freelanced as a technical writer with them for a month. The rate I charged was by the number of words I'd write, not by hours spent. Prior to this, I worked at Betterworks (where we have an OKR platform and employee engagement software offering), where again it was never about the number of hours. It is only fair that you be paid based on work delivery and not by how long you spend in front of a computer screen. Moreover it's COVID, and when people work from home it is highly likely that they'll need to get away from the screen very often, for doing housework or errands or any of that sort.
So like you said, if you have an OKR software and some project-management software like JIRA (or hopefully a better alternative) - and that's it, you never need to track anything else. Employee tracking software is just super intrusive, patronizing, unnecessary and creates a culture of distrust and fear-based management. Moreover people will find ways to evade it all the time. I can easily watch YouTube or browse Facebook on my personal laptop or phone should I be inclined to do so.