I definitely agree with this.  I think the plasma vortex is the same basic propulsive principle. Once you get to millions of volts charge on a surface you can’t help but have ionization of the surroundings.  In either form, enveloping the craft or a contained plasma vortex within the craft both produce thrust by creating a high energy plasma with millions of volts of electric potential between the craft/engine and surroundings.  I think the internal vortex engine would be less stealth and travel slower because the entire-craft-encompassing-version creates a faraday/cooper-pair shielding effect from air/medium friction and allows transmedium flight (possibly up to and including through solids). To the stealth point, we already charge the hulls of conventional craft to produce a plasma across the surface that significantly reduces radar signature.