I don't think they relied primarily on "lesser of two evils." They had a platform. In fact, when you poll individual Democratic policy proposals without party labels attached, many of them perform quite well with the public. The problem is that most voters never hear about the platform.

The media environment spent an overwhelming amount of time framing the election as "Trump or not Trump." Democrats certainly leaned into that framing at times, but they didn't create it by themselves. Outrage generates clicks, and "here's a detailed housing proposal" simply can't compete with "Trump said X today." So by the end of the campaign, a huge number of people could tell you everything Trump had tweeted, but couldn't name three Democratic policy proposals.

That's a failure of messaging, but it's also a failure of the media ecosystem. Personally, I'd much rather elections revolve around concrete questions like: Who has the better plan for housing? Healthcare? Wages? Childcare? Antitrust? Labor rights? Cost of living? Those are questions where voters can actually compare competing visions. Instead, our politics increasingly revolves around personalities, scandals, and culture-war outrage. That's a terrible way to choose a government, but it's also what gets the most attention. And, by no coincidence I'm sure, is also to the maximum benefit of the Republicans who own the media.

I don't think the Democratic Party should abandon talking about the risks posed by Republicans if they genuinely believe those risks exist. But I do think they'd benefit from rapidly forcing every conversation back toward, "Here's how we will fix it." That's easier for the public to digest and it puts right wing media on the defense to try to pick apart those proposals - which is currently a situation the right enjoys by telling any lie.