So it is possible that either Sidious had more force potential for whatever reason, or he had access to teachings of greater quality than Yoda did.
Based on what we know, it seems to be the only options.
You also have to take a look at how high he lifted them. Maybe 1-2 feet? And perhaps he did get cocky but his look of shock was more like "I can't believe he was able to stop it and throw it back at me". And the fact that Sidious jumped down was because he couldn't stop it, rather him not taking the fight seriously. If he DIDNT take the fight seriously, that was the moment he did. And sheer physics demonstrate that what Yoda did compared to Sidious, demonstrated his superiority over certain aspects over the force, compared to Sidious.
One to two feet? I would recommend reviewing the fight again.
Palpatine ripped three pods from their moorings, and tossed them into the air, behind him, giving them extra momentum when he threw them at Yoda. No, it was several meters.
Also, after the final pod was thrown, Sidious was so wrapped up in his amusement, that he was not paying attention, nor did he take the fight seriously at all. If you'd like to go on expressions, when he finally did pay attention - the curious tick of the head and the "eh?" that he muttered seemed to hint at confusion, at how Yoda managed to stop it and throw it back.
Look carefully bro. The first second or two of the blast Yoda is shown grimacing. Then he turns back around and puts on his "you're ******" face. As soon as that happens he is seem absorbing the lightning, and Palpatine is showing the "i'm screwed" look, and more and more he seems to be either getting more deformed, or losing control of everything, until the blast pushes them both away. This also shows that Yoda was winning and Sidious was at the end of his ropes.
I am listening carefully. Once again, you're incorrect.
Yoda starts off, grimacing in pain and effort, with Sidious once again laughing. This seems to piss Yoda off, so he starts to move the lightning back, and then Sidious gets the "I'm screwed" look.
And, as I've already proven, this does not determine Yoda's superiority. For the vast majority of that scene, Palpatine had the advantage, and was overpowering Yoda. Only at the last moment did Yoda manage to act, and all he did was simply push the coiled energy directly in between them - which explains why both of them were knocked back by the shockwaves.
And this is why I don't understand how they can consider a man, who up to that point had only force lightning(which is all he ever used), the most powerful sith lord in history. That just tells me that it disregards the EU..
Considering how he was cited as such in EU sourcebooks, that's a poor assessment.
Is it stated that he didn't practice in 13 years?
Yes. I'd recommend reading the RotS novelization. He had his lightsaber contained in a neuranium statue for the better part of thirteen years.
Also, we know Yoda teaches children saber forms, but honestly when is the last time Yoda picked up a saber, prior to Dooku? It could have been 50 years, or 100 years for all we know, right? If that were the case, then Yoda was out of practice to, seeing as he had no reason to use a lightsaber up until fighting Dooku.
That is precisely my point.
Yoda, as an instructor, master, and Grandmaster, actively practiced with a lightsaber. There is no refuting that. He trained with the younglings, Dooku, and several others. Darth Maul: Shadow Hunter specifically states that he engaged in practice duels often. I would recommend familiarizing yourself in PT era novels a bit more.
Sidious had none after TPM.
And again I don't think it had as much to do with force potential as it did with the amount of Knowledge that Sidious had, and its quality that surpassed Yoda's. I'd like to think they were both at their respective peaks in ROTS in terms of equal knowledge and what not, and Yoda clearly proved to be more powerful than Sidious.
The point is: Sidious's potential > Yoda's.
Sidious had, perhaps, sixty years of training in the Force, whereas Yoda had eight hundred and eighty. And he was only able to stalemate Sidious.
As I told you, Yoda was at his peak. Sidious was not. That is a poor assessment.
Edit, regarding Sidious's lightsaber abilities:
"In Episode I Journal: Darth Maul, he demonstrated the ability to "move faster than {Darth Maul's} eye can follow," and wielded a lightsaber with such precision that he traced Maul's outline with its blade so closely that "one flinch, one involuntary twitch of a muscle" would have killed him."