It depends on how competitive your niche is.
If you are in a fairly obscure niche with only a handful of websites dominating your sub-niche, you probably can get away with only content.
Now just because you're not building backlinks doesn't mean that you can let your guard down and try to coast.
This definitely doesn't mean that you have a license to post garbage content and somehow, someway you outrank your competitors.
It doesn't work that way!
Instead, when you are in a fairly low-demand or low saturation niche, you are presented with a tremendous opportunity to beat your competitors solely on content quality.
How do you go about doing this?
Well, first of all, you need to reverse-engineer your competitors.
Find their easy-to-rank keywords that pull in a decent amount of traffic.
Dominate those.
Rank for those so your domain goes up in authority.
That's the first step.
But the key to this is to produce superior content.
How do you know that your content blows away the competition?
First, you use a content optimization tool like Frase or SurferSEO.
Your content will have contextual keywords that your competitors might not have even included in their content.
Next, you have to deliver on search intent.
Put simply, the target keyword of each of your articles has an intent behind it.
People use that specific key phrase instead of others.
Why are they doing that?
Understand the answer to this question and deliver on the expectations of the people entering those keywords into Google.
If you're able to do that and your content is more comprehensive, more up-to-date, and is formatted in such a way that it's easier to read, chances are, you will outrank your competitors.
Does this mean that your content has to be longer?
No!
That's a common misconception.
Just because your content is longer doesn't mean that it's better.
Your content has to have proper context and more importantly must deliver on the intent behind the keywords you're targetting.
That's how you play the game to win.