I'll add my little impression based on your #5 video. The idea of having additional lightning strands around the center orb that don't reach out to the walls is a nice comment. But, here' my issue. While looking at the animation in mid air, no walls, the lightning orb seems boring because I am comparing it to the very first video that I actually found wicked awesome. Seeing those lightning bolts attached to walls from the center orb is just brilliant and nice. I have to agree that it does feel a bit weak. What is fun to see in your bolt is how it attaches to your walls and in #5, we kind of loose it, so we need to stick most of the stuff near your orb and not spread it out too much. To add power, these are my suggestions:
1. Instead of having straight lightning bolts going nowhere, your center orb should have circular electric bolts trying to reach out, but sticking to the center. Basically, the bolts should try to go out but curve back on the orb as there is no walls near.
2. Your #1 video impresses me because I feel in the bolt it's energy attracted to the walls and the feeling is awesome so I'd tend to keep it that way when walls are available BUT still use what others commented, add smaller bolts trying to reach out but since the energy is not sufficient for THAT bolt, it curves back to the center. This makes your energy ball look larger without changing the size of it.
3. Now, seing that you seem in early stages, I guess that you will improve on graphics, but I think you should add color to your bolt. Making purplish/blueish lightning bolts with yellowish/whiteish impacts which will make us see the power of each impact on the walls. Now, important, no straight colors, you need gradients, usually, the light is bright (light colored) at it's center and fades out to it's pure darker color outside and fades on it's borders. It may be tricky to do that, but a single line of blue or purple will look too cheap, but it's a start in an early stage.
4. A nice dissapearing particle system would add to the life of your ball. Every strike on a wall should produce a small number of whiteish/yellowish particlkes that drop on the ground and dissapear going from bright white/yellow to orangy/dark red then fade away as if it cools down.
5. Also add little spark particles that go out in all directions from your center ball, this would simulate the straight bolts suggested BUT with NO bolts attached to those sparks, just bright sparks particles spurting out of your orb and fading away but not too much as you already have a lot going on with this nice lightning orb.
6. A gentle trailing smoke tail would also add to the effect of sending this orb out. Basically, orb sized smoke and reducing to the center while the orb gets further away. GM's particle center can do this easily without any calculation. I used it with fire once in my DaRic Lost Explorer 2 game. It generates particles mostly in the center which fade away. This produces a trianglular shaped effect without you even thinking about positioning them properly, GMS is hot!
7. Add a small explosion impact with a larger bright light on the surface of your wals which show the power of each bolt hitting the place. Of course, you want that effect to be quick and lightning fast or else your wall will be completely white with a very fast dissapearing smoke effect on the impact area.
8. Finally, add a bigger explosion impact on the wall when the actual orb hits it showing that the energy has been hugely dispersed at that spot, you can even add a short flamming effect as if on impact the orb burns and dissapears in smoke.
This would be beautiful and add a lot of life to your effect which I already find brilliant and well done up to now!