If that were true they had plenty of time to pack the court themselves, but they haven’t.
It is correct to say that they have had plenty of time to provoke a constitutional crisis. It is also correct to note that they could have resorted to abusive procedure even worse than the one they already did. Which is like saying they created a category four hurricane instead of a category five.
Note that Trump and McConnell are rushing to fill the Supreme Court, despite 4 years of leaving about half the government posts vacant.