$8,400 over three years is about $230/month. And aside from the opportunity cost of your labor to optimize that, you should also theoretically account for any purchases that you wouldn't have made if you weren't trying to optimize your points (if any; I'm sure it's hard to attribute).
With current interest rates of around 5%, one could get the same stream of income ($2.8k/y) by just plonking $50k or so into a high-yield savings account or money market fund.
I have likely spent 1 hour applying for cards, loading them into Apple Wallet over 3 years. If you are doing the math on opportunity cost for something you spent 1 hour over 3 years, you are already wasting your time.
To be honest, the $50k argument isn't comparable. It's like saying "Oh you have a side gig making $10k/year, why don't you just invest $200k in a money market fund instead?" First, someone could do both. And second, it's not even a logical comparison.
With current interest rates of around 5%, one could get the same stream of income ($2.8k/y) by just plonking $50k or so into a high-yield savings account or money market fund.