Not just less, there would be none and it would have all been given out as dividends. Stock buybacks are just dividends reinvested in the company for you.

Dividends would have been taxed. “Stock buy-backs are just...” leaves a lot out, enough that one might wonder if it were intentional.

The company buying back their stock had to buy it from someone though and that person who sold it is going to pay a tax on any gains from that sale.

I bought way too high, so when I sell my AcmeCo stock back to AcmeCo, I’ll get a tax refund!

If you want to tax profits, then tax profits. If you want to have cheesy loophole tax avoidance, stock buy-backs might be more your style.

Then how about the company doesn't make that investment decision for me?

You can sell a proportion of you holdings to maintain the same ownership percentage thus acting like a dividend if you want. With fractional shares, you should be able to even do it with a small amount of shares. Albeit, I don't know of any brokerage that automates it for you. You can also just buy ETFs as they will sell stocks themselves in order to maintain proper weightings.

Then sell proportionately to the buyback, you'll probably even make some money to get taxed on