In his letter Hearn says.
Jeff Garzik and Gavin Andresen, the two of five Bitcoin Core committers
Are there really only 5 Bitcoin core committers? What is a bitcoin "core committer"?
How did these people become part of the 5?
it doesnt mean bitcoin-core. the program.
it means 5 main people who add the most to the bitcoin ecosystem.
EG hearns bitcoinJ was used alot. and to be able to understand bitcoins initial code(in c++) to then replicate it in java is no simple task.
alot of people are hooked on the idea that "if its not bitcoin-core.exe, its simply not bitcoin".. which is just playing into blockstreams agenda of taking over the bitcoin brand.
there are many implementations that are not forks, that work with bitcoins current rules, and bitcoins current chain/genesis without issue... but these other implementations only vary in either programming language type(c++,VB,C#,java), GUI visuals or other features, so bitcoin core is not the only program that fully works. and bitcoin-core should not be the only choice, ever