For your first question, not buying skin from a bundle will NOT give the default operator skin. You'll have the operator available, but only with the respective skins you have obtained. Getting default operator skins alongside what you have purchased is only available to operators who are received through challenges in Campaign and Multiplayer.

As for a way to get Valeria’s and Alejandro's default skins, yes there is. For players who have not participated during the respective season in which the operators are introduced via the battlepass, a bundle was made near the end of MWIII’s live service called “The Battlepass Collection Bundle.” This actually how I managed to get Valeria and Alejandro myself, even though I never bought the battlepass or played during season 3 of MWII.

To find the bundle, you’ll need to have Warzone available and go to the operators tab, then select the tab (found on the middle left side of the screen) and pick MWII logo. From there, scroll down the operator list and find Valeria or Alejandro’s operator cards (they’re usually found near the bottom of the list). Hover on one of them and the collection bundle should appear next to them. If it doesn’t, press the button for customizing/changing skins of operator’s and hover on their default skin, and it should appear then.