This 2008 page was referenced in 2010 in other places…
Selfish mining does not exist. There are other attacks that could be used. And the time would need to be less than 1.5Sec. The maths is not symmetric as people think. So, as you lower the rate, you need to have faster and faster transmissions and at a point you start running into physics.
Settlement is 10 mins.
In Visa it is 60 plus days.
The TX can be added in under 2 seconds safely.
There are also issues with what you suggest. Shorter block times change the nature of the rewards. Have a read of:
Yes, I was told by some of the Core people that I only understand Bitcoin as it was and not as it has become.
I hope that I never understand what they want it to become to be honest. I will stay with the original vision.