For 32 years I simply purchased packaged tapered leaders and went fishing. My leaders ended up being a mess of knotted sections as I replaced lost leader length and tipped section. Using graphite rods I was able to power through whatever butt section the packaged leaders were made with. Then I built and fished a reasonably fast (yet still slow compared to graphite) bamboo rod. The rod performed poorly, as I wasn't able to turn leaders over. While lawn casting I observed the fly line energy being killed by the leader. Presenting dry flies had been frustrating, especially if I was casting under overhanging trees.
A search of the classic bamboo forum came up with a reference to making the butt section of your leader similar in stiffness to the stiffness of the end of your fly line. I had nothing to lose and quickly compared the stiffness of my DT four weight line tip to the stiffness of my leader and the leader was much stiffer. I'd started making leaders in 2015, so I created a leader with a 15 pound initial butt section - this made a world of difference on the four weight bamboo rod, and also on a three weight graphite rod.
I think there is something to the suggestions that leader and fly line stiffness be reasonably close. Maybe not as noticeable when fishing fast rods, and maybe more noticeable with slower rods.
Jeff