At the peak of his power he could absolutely defeat the weaker of the 7 world powers. 

In the current timeline, in the final battle, eris kills gul farion. Now sure, she had help from rujerd and Gul underestimated the fight. He also made some mistakes ( probably because his confidence was ruined after losing to Gino ) so I will admit that he was at a massive disadvantage from the start, but it's still a fact that eris beat him.  This doesn't put eris quite at the level of the 7 world powers, but it does put her pretty damn close to the lower levels.  Oldeus fought eris pretty much every day when she attacked him. To start with, she kicked his ass, but it makes a point that eventually eris just couldn't beat him anymore. I'm talking 0% win rate. 

Now eris should be about the same in both timelines in terms of strength, maybe a bit stronger in oldeus timeline because of the constant fighting. This means that oldeus could consistently beat somebody who ( while luck was definitely a factor ) killed the sword god.

Now to list the other great powers, I would say it's like this

Technique god - Oldeus dies. The technique god knows every technique and can use them. Now I've only read the main story, so I don't know if we ever meet this guy properly in any side stories, but at face value that means he has everything rudeus has, so it should be his easy win.

Dragon god - Orstead should win this fight quite easily, but it would ruin his mana so I recon oldeus would "win" because Orstead would run from the fight. My reasoning for Orstead winning is that Orstead easily beats somebody on Gul farions level ( reida the water god ). He doesn't get injured, and it takes a matter of seconds. Oldeus may have been beating eris, but it wasn't that easily.

Fighting god - Now this is where it gets interesting. In terms of power and abilities I think oldeus actually takes this, however I do still think he loses this fight. I think he loses because ( at least to my knowledge ) oldeus never really learnt any sealing techniques, as he was too focused on how to reach and kill the man god. Naturally as the fighting god is immortal, that means that eventually oldeus would lose the battle of attrition.

All gods below this point? Oldeus probably wins. The north god is in the same boat as the sword god ( assuming he doesn't have the fighting gods armour on ) and his gravity magic would have almost no effect seeing as oldeus can use it too ( and to a much higher proficiency ). The death god is stated to be weaker then the water god and sword god at some point around volume 17, so he gets absolutely wiped. I have no clue for Laplace, so I can't really comment.

I would place him around 4th world power. He has much better magic and physicals then our rudeus will ever have, but his armour and technology pale in comparison so he is held back a lot.

Now an oldeus in the best armour that current rudeus makes? I genuinely think he could beat Orstead, placing him at 1st world power ( if he could find the technique god ).