To be fair that was before I got to the discussion how a double weakness doesn't hold a mon back.
Though I'll agree that if they made a Poison/Electric defensive Pokemon it could be good with the right stats (and maybe Ability), the two counter examples you gave have some other things going for it:
Magnezone has 11 Resistances plus its Magnet Pull Ability makes it an excellent Steel-type trapper (note many sets before Gen VIII had it needing HP Fire, and Gen VIII may have gotten rid of HP Fire but gave it the amazing Body Press).
Heatran is a Legendary so it has a high BST to work with. If a com mon had 91/106/106 defenses, even if it was given a low Speed, it would still be struggling to give its offense stats a good amount of points at least without a case of min-maxing. But since Heatran is a Legendary with a 600+ BST, pfft, it still has 297 points to work with, 220 points after giving it 77 Speed.
Almost all good defensive pokemon and good stats and abilities. Just look Duraludon,
As i have said earlier, Eelektross with a secondary poison type would be busted. Having only one weakness, one immunity and 8 resistance is too much even with mediocre bulk.
But even if we take it ability levitate and give it something like volt absorb, intimidate and regenerator. And give a more defensive stats spread like 100/60/100/105/100/50 it would still be OU tier. Even with any recovery.
Of course if it had bad stats it would be shit but so would any other mon.
Just give toxapex electric/poison typing and it would be as good as original pex if not better.












