Stefano didn't shut Lexie in the tunnel at risk to her health. EJ did. It shouldn't have been rewritten.
Stefano wouldn't ditch EJ for not being his bio son any more than he ditched Tony or Kristen or Peter. The rewrite that Stefano raised Tony and not EJ to justify it was equally stupid... because Stefano DID raise EJ and did NOT raise Tony.
The DiMeras walking every time they do something atrocious is an ongoing problem for Days. Days would be well-served by using some short term villains and having the good guys win out and the bad guys jailed or killed off for a while.
But this was not the wya to rest the DiMeras.