Yep, that's my take. Especially with the broadcast tower being directly above the vault, I think it just made much more sense to them at that point to just beam the plans up rather that risk fighting their way out of the complex, running across the beach, flying a ship through TIE squadrons (basically doing everything that the first teaser showed.)
Also their original plan of escaping by ship was under the assumption that there'd be no rebel fleet to beam them to in the first place.
After they sent the plans they only had to discreetly make their escape with much less urgency...until they saw the approaching blast wave.
Which gave some real poignancy to the ending. If this weren't a prequel to a pre-existing story you would expect Jyn and Cassian to be the ones who go on to actually destroy the Death Star. Instead they die, never knowing if their sacrifice will actually be worth it.
The Empire lived on anyhow and became even bigger and badder- so much for the old Rebellion!
