These are the top 4 defensemen of the final 4 teams in the Stanley Cup playoffs for the past 3 years. Finalists bolded. Champions Italicized. This year's are alphabetical because there's not a winner yet.
2019
San Jose Sharks - Justin Braun (6'2"), Marc Edouard Vlasic (6'1") , Brent Burns (6'5"), Erik Karlsson (6'0")
Carolina Hurricanes - Jaccob Slavin (6'3"), Justin Faulk (6'0"), Brett Pesce (6'3"), Dougie Hamilton (6'6")
Boston Bruins - Zdeno Chara (6'9"), Charlie McAvoy (6'0"), Brandon Carlo (6'5"), Torey Krug (5'9")
St. Louis Blues - Alex Pietrangelo (6'3"), Colton Parayko (6'6"), Jay Bouwmeester (6'4"), Joel Edmundson (6'4")
2020
Vegas Golden Knights - Shea Theodore (6'2"), Alec Martinez (6'1"), Nate Schmidt (6'0"), Zach Whitecloud (6'2")
New York Islanders - Ryan Pulock (6'2"), Adam Pelech (6'3"), Scott Mayfield (6'5"), Devon Toews (6'1")
Dallas Stars - Esa Lindell (6'3"), John Klingberg (6'3"), Miro Heiskanen (6'1"), Jamie Oleksiak (6'7")
Tampa Bay Lightning - Victor Hedman (6'6"), Ryan McDonagh (6'1"), Mikhail Sergachev (6'3"), Erik Cernak (6'3")
2021
Montreal Canadiens - Shea Weber (6'4"), Ben Chiarot (6'3"), Jeff Petry (6'3"), Joel Edmundson (6'4")
New York Islanders - Ryan Pulock (6'2"), Adam Pelech (6'3"), Scott Mayfield (6'5"), Nick Leddy (6'0")
Tampa Bay Lightning - Victor Hedman (6'6"), Ryan McDonagh (6'1"), Erik Cernak (6'3"), Mikhail Sergachev (6'3")
Vegas Golden Knights - Alex Pietrangelo (6'3"), Alec Martinez (6'1"), Shea Theodore (6'2"), Brayden McNabb (6'4")
Just looking at the data, in the past 3 years, 48 defensemen have made the Stanley Cup Semifinals. One was sub-6 foot. Five were 6 feet flat. The average height of a defenseman was 6 foot 2.875 inches (just a shade under 6'3").