It all depends on how fast you make progress even if you spend, say, 50% of your time building. If the progress is so slow that people feel they have to loot more to survive the next horde, they will do that. Not because it's the most efficient, but because they feel they have to.
Of course, players who only loot will have a much faster progress. And this is where balancing comes into play.
As long as the developers don't forget that building still exists and don't throw it out of the game because nobody builds anymore anyway.
That's always my fear when aspects of the game are neglected. The developers might feel that it is unnecessary and can be removed.