some of my users are complaining that theme is not very user friendly.
And they recommended that as a better alternative? That black on blue combination is something else.
My recommendation would be to role with Lavender, then adjust the theme to match the dark theme you're going for. I had a lightbulb in my header that switched between dark and light on my old theme. Will do it for persona at some point. But I'm in no rush.
I think lavender theme does not support custom skins like persona.
Not as well, but the bootstrap custom skins are a bit flaky anyway. IMO obviously. If you want a theme you're happy with. You'll have to roll your own or get the nodebb guys to quote you for the work. There isn't a one size fits all theme unfortunately unless you know how to write CSS.