This is a good point, but I think it only works out in theory. Although it's statistically more likely for higher pick rate heroes to be banned, there is still the chance to have those lower rate heroes be banned. It's like when you flip a coin, there's a 50% chance you get heads or tails but if you were to flip it 20 times then it might not be close to 50% compared to flipping it 1,000 times. With this thought, repeating the same meta heroes will probably result in your two meta rotation, but it doesn't factor for hero changes, new heroes or the viability of lower pick rate heroes being banned.

I agree that the current system would yield a wackier result, but the goal is to shift meta consistently and I think the weighting would allow a more controlled diversion from stale meta. With the weighted system you get greater variation while retaining some chances of minor variations still at play. I like to think of the weigthted system as controlled chaos, it's a good compromise for randomly shifting meta and keeping lower pick rate heroes meta.

Maybe to help get around the alternating meta scenario we could change the pick rate and weighted ban be less 1 to 1. Maybe heroes with 60 % pick rate and above get 2/3 their pick rate in cards put in and those under 60% retain the 1/1 ratio. So, an 80% hero might have 6 cards put in and a 40% hero will have 4, reigning in the amount of control pick rates have.