@AniMangelo I am not sure why you are repeatedly comparing this Pokemon to Rotom Wash as if it is its only competition, but I'll address each of your points individually anyway.
1: Eelektross's movepool is better, but that doesn't mean that its competition won't get equally serviceable options for moves. Pokemon like Mega Manectric get by with Flamethrower and HP Ice and are regarded as having good coverage, even when that's more or less the extent of their movepool. If you want to compare to Rotom Wash, then it gets a second STAB, Will-O-Wisp and Pain Split all of which contribute to its role as a pivot. I do not see how Giga Drain is more reliable recovery than Pain Split.
2: I disagree. With its part Water type Rotom Wash gains key resistances to types like Fire, Water and Ice which massively improve its switch-in opportunities. Grass is an uncommon offensive typing outside of Pokemon that get it from STAB -- Fire, Water and Ice show up in much broader contexts. Pure Electric + Levitate is also good but it's not better as you say.
3: Such as...? My point stands that even though Eelektross has good stats, other Pokemon with better a better Speed and typing outclass it. Magnezone, Tapu Koko, Rotom Wash, Zapdos, Raikou etc. all do their roles better than Eelektross would.
4: Rotom Wash is not better than Eelektross offensively (I never said it was!), but again you're ignoring Pokemon like Manectric, Tapu Koko etc. as if they don't exist. These Pokemon are faster, more powerful and have good enough movepools that Eelektross doesn't have anything huge over them. Rotom's defences are no worse than Eelektross's because it has better Defence and Special Defence, and it isn't pressured to invest in an attacking stat as it poses more of a threat spreading Will-O-Wisp and gaining momentum. Burning the opponent indirectly boosts its Defence, and it can use Leftovers and Pain Split unlike Eelektross if it depends on Assault Vest. Combined with more switch-in opportunities, Rotom Wash makes for an all-around better pivot.