At the risk of opening the can of worms again and going against my own advice...
Who saves Shepard's body from the Collectors? Who finds the plans for Crucible and has the most to do with defeating the Reapers, second only to Shepard? Who is the spokesperson for this cycle if Shepard fails to stop the Reapers by picking Refuse?
It's not you who makes the deuteragonist, but the story, or rather, Bioware. And they made Liara deuteragonist.
So? If it weren't for Tali we woudn't even know the Reapers existed until it was too late, if it weren't for Mordin we would've never even beat the Collectors etc. etc. . The deuteragonist isn't determined purely by his/her actions or relevance to the overall plot but also screen time and relationship with the protagonist. By that criteria alone, Anderson, Hackett or TIM would be deuteragonist/triteragonist.
Being the person who speaks in the Refuse epilogue is utterly meaningless. Liara being the "second most important person to defeat the Reapers" is highly debatable.
No one made Liara the deuteragonist by default, you're just blinded by your own bias.