How exactly will this prevent any hacking from the blockchain level?

I'm not sure what you talking about. If you mean bugs in the blockchain code, lock ups don't prevent that either. They prevent people who get access to keys (for example by exploiting the web site) from performing transactions. 2FA would provide pretty much the same protection.

The savings feature works only for STEEM, not STEEMPOWER

Yes, I was suggesting that it perhaps be changed to work in a more useful way since the existing feature is almost unused. Again, an experiment which failed, so we should move on and try something else.

by turning a screw without asking whether or not the screw is at the right place or if the screw breaks if we turn it more.

I don't agree we are doing that. IMO we are thinking about what could break and concluding that nothing would. In part we are also looking around and seeing what several hundred other active blockchain projects are doing and seeing that they do just fine without months of lockup in the base layer.