naming wise depends on how deep you want to get into it and what true classifications are in say actual agriculture and science vs us home growers, as there are points that are out there for definition.
But in our past and terms used in the community F1 is and has been acceptable, really so long as you can follow and express that to others if need be is all that matters on a base level.
As for crossing to clones vs another strain expression , the clones will be most like the parent and the vigor aspect is more apparent in further generations but imo is no different than within the same strain.
As for that F1 being unstable, actually id say its the opposite in that what comes out is usually pretty even, its on the next generation that things diverge and you get to see more distinct expressions.