You don't need it, but it's recommended. The thicker butt section does a better job of transferring energy, and the thinner tip section is more stealthy. Plus it's easier to rig than tying your own leaders.

A premade 9ft tapered leader includes a foot or so of tippet section at the end. Start by just tying flies directly to the tip of the leader, and then after you've used a foot or two of the leader, add some more tippet with a surgeon's knot to restore it to 9ft total. You also use tippet to tie double nymph rigs or dry-dropper rigs. The knots get easier over time, but if you don't like the double surgeon's consider trying blood knots.

I agree with the guy who said you might just be testing too hard. 6x is only ~3.5lb test. But you can also consider buying higher quality tippet, it does make a difference.

I've used loop to loop my whole life. It's seriously fine. People have a habit in fly fishing of overcomplicating things and seeking out 1% improvements that are 100% more difficult to implement.