As I've said before to this sort of starry eyed delusion of Beto's invincibility predicated on what seems to be anecdote, I completely disagree as there is no evidentiary basis to this. He doesn't have the charisma, the polling, or the bona fides to dominate what promises to be a crowded field full of popular Dems. What star power he does have is almost entirely an artifice of a media that has essentially done nothing but shill for the man.
You know who is actually a progressive voice in the deep south who lost his race but achieved far more in terms of making inroads with conservatives than Beto did in a much more hostile district (possibly the most hostile of all)? Ojeda.
With regards to the media, I'm not saying that there's some kind of smoke filled room where they're engaging in a devious scheme to push Beto, but the fact of the matter is, pretty much every mainstream outlet I know of that isn't Repub aligned has been tooting this man's horn essentially without causation over all others lately; convergence rather than conspiracy, but one that's surely motivated by his alignment with establishment politics given the other people they could be talking up. Moreover if you're looking for change you'll be disappointed as this strongly implies Beto is essentially more of the same; more status quo prosaic Obama/Clinton style neo-liberalism that they champion tirelessly.
And yes, it absolutely does bother progressives that he is not yet on board with MFA; if you haven't been paying attention it's definitely something of a litmus test. Beyond that, there are indeed shades of Obama all about this guy where he puts on the facade of progressivism only to abandon that more or less immediately the moment he hits office, governing as a standard establishment Dem; y'know, the sort of thing that saw the Dem party utterly routed in 2010 and beyond? That made a Trump win possible? That too concerns us, and it should furthermore concern anyone who cares about the long term prospects of the party, rather than scoring a short term win for their internal faction.
Also where's the proof that we're going to be stuck with another status quo donor friendly corporatist as nominee (what you nominally term as 'centre left')? The only thing that even begins to suggest this is Biden's polling, but the guy is no sure bet, even assuming he does run. Moreover I think it's hilarious that some people still identify what are commonplace, successful policies and programs in the rest of the developed world as being 'far left'. Jesus christ, it's not that Europe, the Commonwealth and the rest of them are far left raging demi-communists, it's that we've flirted with the lunatic fringes of the right, and have been pulled ever further in that direction for decades upon decades; the United States' Overton window is the one that is skewed, not that of the rest of the free world; by any reasonable standard a 'centre left' Democrat is a bona fide conservative at best in a sweeping majority of developed countries.
I mean if it comes down to Beto vs Trump, god forbid, yeah, we'll pick Beto reluctantly (but not as reluctantly as we might pick say Hillary); however I suspect a majority of us won't be happy about it at all given there are far better candidates that appear to be poised for the nomination process; Ojeda who has officially declared is already a markedly superior option.