so... is Luke the most powerful jedi of all time

Luke. Won reborn overpowered Palpatine in lightsaber combat and by LOTF he got even stronger. And there are many more examples to prove.

Originally posted by darkriddle
Luke Skywalker's powers seem to change from book to book, which I suppose is reasonable. He is able to stop an ATAT walker in the graphic novel Dark Empire with telekinesis, and much later defeats Darth Ceadus, who has traveled the galaxy to upgrade his skills. In fact, he learns that "Teleportation-thingee" power faster than Jacen did, or so they say. He also learns to astro-project and gets even more knowledge from the Wills (is that right) and The White Current. His new fight against Abeloth will definitely test his powers though.

It's a good thing, otherwise it would be too boring.
Post DE Luke gradually started using less and less force and let other students do the job. He was mostly passively meditating and as the result got much weaker. Although, It almost costed him life, when he faced Lord Nyax, nevertheless, he's learned how to use force in right way without unnecessary exertions.
Confrontation with Baron DO Sages leader is very good example.
Luke used just enough force to absorb electric judgement with lightsaber and didn't try to do any counter attacks. When Kel Dor started making powerful force tornado capable of tearing pillars apart, Luke simply rooted himself in place and did couple of force pushes to split focused current attacks. Then Luke threw torn off pillar into Kel Dor and, while foe's concentration was broken instead of using some other force powers, Luke simply ran to him and kicked. Kel Dor wanted to continue but simply collapsed face-first from being exhausted from over-exertions.
Imho it was great example of using force wisely and doing less effort to defeat strong opponents.

It's quite possible. Luke was the only jedi that Jacen Solo feared while he was Darth Caedus. That makes him the most powerful jedi of the time. He battled and defeated many powerful enemies. He was able to kill several Yuuzhan Vong warriors at one time, a feat that is often not given the recognition that is deserved. He is fighting highly trained and skilled warriors who are not part of the Force and who's armor and weapons are able to withstand a lightsaber. He also defeated the Yuuzhan Vong Overlord and many Slayers(elite Vong warriors) guarding the Overlord.

Luke was also exceptionally skilled in combat. He was a gifted lightsaber duelist; one example is his defeated of Darth Vader, who, I point out, was still good enough to defeat jedi who escaped the Purge and scare almost every enemy of the Empire. Luke created his own lightsaber form and he mastered several lightsaber forms. His skill with a lightsaber would most likely rival the prowess of that of Mace Windu, Kit Fisto, and other masters of the Old Jedi Order.

Skywalker had a large arsenal of Force powers, some of which few jedi in the old Order possessed, and almost none possessed the magnitude which he did. His reactions were incredible and he was able to walk across lava. Like the famous Jedi Master Plo Koon, Luke was able to conjure up a varient of Sith Force lightning, which is called "Electric Judgement". This is one of the rarest Force powers, and a truely incredible Force power. While it is not true Sith Lightning, it is very powerful. Luke was able to merge with the Force once as well. Like Mace Windu and the Solo twins, the Grand Master of the Jedi Order possessed the ability to percieve shatterpoints.

Luke was also a phenomenal pilot. He destroyed the first Death Star. I find that he his a rival of Wedge Antilles, Rogue Leader after Luke stepped down. 😮‍💨

So yes, he may be the most powerful jedi ever. However, cases can be made that other prominent jedi are more powerful.

zoom3, you gave a few good points but, if Luke's lightsaber skill was most likely rivaling Kit Fisto, then Palpatine would turn upside down in his grave from embarrassment. 😆

Luke actually merged with the Force more, than ones. First time, when fighting with reborn Palpatine. Second time during the fight with Slayers. Third time, when Abeloth wrapped around him, he called on the love for Ben and others, light emanated from him weakening her and allowing him to kill her. There were several more miraculous things but don't know if they could be considered as oneness with the Force, since it didn't involve fighting.