Liquid Glass is more than just the transparency. There are many other changes that cannot be disabled that way. Not to mention the overall lag compared to Sequoia (I skipped Tahoe entirely so I had a direct knife-edge transition). 27 is less bad than 26 but Liquid Glass doesn't make anything better than prior UI and makes several things worse, even if you turn down the transparency.

I imagine that the UI changes since Sequoia regarding the giant buttons and whitespace are because Apple plans to release a touchscreen laptop (most rumors say it will be announced tomorrow) so they've decided to make the UI touch friendly at the expense of bloating the UI for everyone who doesn't have a touchscreen. Microsoft made this same decision with the Windows releases after 7.

The rumors also said it would be announced today, so we'll just have to see. Even a broken clock is right twice a day, after all.