The problem we run into here is that those you have listed, including Beto, are all white men. And there are a lot of voters in the Democratic bloc that do not trust white men and will vote for anyone else first. We have a lot of voters who don't do any research on candidates and when they go to vote they will choose by name. Are they a woman? What race are they? That's how they decide. We need to somehow change that and get people to vote for the most electable candidate in November regardless of age, race, gender, etc. It doesn't even have to be the most qualified candidate, but the one who stands the most chance of winning against the R. I mean that's how Trump won. He's not the most qualified, he was the most electable. It's not the ideal way, obviously. The risk you run when you take that path is you end up with someone like Trump whose incompetence keeps getting exposed. Will it harm the Republican party? Probably not. Will it harm the country? Absolutely. So the trick is finding someone both electable and capable.
I tell people who start to spit on older white politicians that that is the demo for the people who built and use the system to their advantage. It's easire to break a good ol boys club up from inside if you infiltrate it as a good ol boy. Our opposition by their very nature do not see anyone else as their equals, other than other white males (and somehow Cruz has worked around this). So with that in mind, all the other electeds are fighting just to gain respect, much less get their voices heard on specific issues.
And that good ol' boy persona rates pretty high in Texas.