There are various reasons that the Elite 4 in Pokemon Crystal do not get stronger. For example, the game is intended for a young audience and it may be too hard.
the elite 4 is in kanto
At the end of the elite 4 he is the champion.
you can go to the kanto region after you beat the elite 4
Train Your Pokemon- (Train till level 60 above,sure can one)
Capture all legendary, train all Pokemon to level 100, Max out stats,
swim left from your home town....have water fall HM with you though...
To complete the storyline you have to beat the Elite 4 To really beat the game you have to defeat Red on Mt.Silver To become a Pokemon master though, you have to catch all 251 Pokemon available in Crystal version
Easy just use a Revive on your stronger Pokemon or trade with a friend to get more strong Pokemon.
After you beat the elite 4 you can battle wally at the end of victory road after you beat him exit then enter and his Pokemon will be stronger
when you finish game(collect badges not get all pokemons) you will saw elite 4(thy are like johto league)in all pokemons.BUT some games like Pokemon silver,gold and crystal(like)have elite 5.The last guy is the powerful Pokemon trainer so get ready.
You have to beat them.
I'm pretty sure it should be the last badge before you go off to the elite 4:)