> Lean is far off the most bloated one. Isabelle most likely takes that spot.
Among these three is the operative phrase here.
I hate to be pedantic, but we are talking about theorem provers here :)
Originally Lean was coded in C++, and dynamically linked executable, if I remeber correctly.
There were some proposals like compressing all the .olean files, but (as far as I know) none of them were implemented. Well, even if some proposals were implemented, their contribution was effectively negated anyway.