I definitely agree that the Gen X crop of Democrats is weak (Kamala Harris, Stacey Abrams, and Gretchen Whitmer are really the only ones I can think of as compelling national candidates down the line, unless some figures in the House manage to build themselves up like Katie Porter) but the millennial crop does have some compelling and appealing figures (Jason Kander, Mandela Barnes, Lauren Underwood) who still have plenty of time to build profiles and experience.
I agree that the party prioritized the Presidential races far too much during the Obama years, but I also think there's a more nuanced side to this. Whitmer and Abrams were both important political figures in Michigan and Georgia, respectively, long before 2018 and spent a long time building up trust and goodwill with both voters and the political institutions in their states, and I'd say it's more a mix of coincidence, good timing, and effective planning that they made their marks in what happened to be a great year for the party electorally.
