Ask HN: Marketing graphic design templates or apps for solo founder?

I'm pretty hopeless at graphic design, but I can manipulate stuff OK in photoshop or sketch. I want to create basic cover photos, heros, etc for use in Twitter, blog posts, Intercom announcements, landing pages, and the like. Not reinventing the wheel, SaaS companies do this all time and usually include a title, half sentence, screenshot/image, and background gradient/color.

Any suggestions? I've tried Envato, but there's a lot of crap to sift through, and the templates are usually too busy.