Does the ending depend upon completion like in ME3?

Viability on its own does not affect the outcome. Doing certain quests does mean you get extra help in the final push (but that only affects gameplay), and . There is an additional small scene if you reach 100% viability overall but that's separate than the ending.

Also note that you can achieve 100% viability without doing all the side quests. Most planets have a "main questline" which allows you to establish the outpost that gives a large amount of viability. Doing that, the monoliths, and will almost get you to 100% viability.