Left or right isn't the issue nor is "speaking to class issues." The one thing a Dem candidate needs to do is speak to the needs of voters period, the vast majority of those voters aren't consumed with 'class issues'. Hillary Clinton was perceived as ignoring the concerns of the Rust Belt, taking their votes for granted and calling folks "deplorables" and she paid for it. Trump spoke to their wants and needs (admittedly feeding them a line of bullshit, but he actually spoke to their concerns and aspirations).
That's why the line about "class issues" is so wrong-headed IMHO. Whether the 1% has more money than them is not a non-factor it's just not what drives people whose actual concerns and needs are much more granular and specific. Voters want a POTUS and representatives who get the basics done - roads built and paved, schools funded, an economy that doesn't suck, not invading somewhere in southwest Asia or Africa. Someone like Buttigieg is doing great because his focus does largely align with the simple good governance/bread and butter stuff like infrastructure. Compared with someone like Warren whose ideas aren't necessarily repelling people, but folks don't vote based upon a 14 point plan to break up Amazon because they're selling their own branded products on the site which is "anti-competitive."