Because a fighter is stronger doesn't mean all his moves are as strong as someone weaker than him. Supernovas high end moves like Luffy's, Law's or Zoro's actually make Fujitora's low end moves like Meteorites or Ferocious Tiger look like shit(mountain vs buildings level, really?). A low end move from even a top tier can easily be weaker than the high end move from a high tier.
Jozu used a similar attack on Kuzan and it was meant to push him out of the way. Compare that to the iceberg lifting feat and they are dimensions apart. The logical conclusion is that he didn't put much effort in that "opening" attack especially since it would go along the lines that someone who had no way to improve while being a sitting duck in prison(with sea stones) was badly hurt from a pre-gear Alabasta Bazooka. Taking a hakified thousand worlds from Zoro is definitely much more impressive and he still took a big part of the 1080 pound cannon too
Meh, I don't see it that way. For fighters like Jozu and Zoro, it is feasible to say that the stronger character's moves are all better than the weaker character's because their arsenals depend on physical strength and force. The power output of their moves just depend on the force they put behind it, they don't have to have the same, universal power output all of the time. For example, Jozu's Brilliant Punk. It's just a slam. A slam is as strong as you make it. Jozu can do a Brilliant Punk that can barely dent a rock, then do a Brilliant Punk that can shatter steel, it all depends on how hard he wants to throw the Brilliant Punk. Same for Zoro. He can do a Lion's Song that can barely scratch stone, or one that will cleave a Pacifista in half. It all depends on how much strength he wants to put behind the sword strike at that time. Jozu could just throw all of his strength in Brilliant Punk and Zoro can throw all of his into Lion's Song, and Jozu will come out the victor because their moves are directly dependent on how much of their strength they choose to put behind the attack. Naming them is just cosmetic. Zoro can do a Lion's Song and then a Thousand Worlds today with the latter being stronger, then do it again tomorrow with the former being stronger this time.
Pica didn't even take a Hakified Thousand World's, he was defeated by a Hakified Thousand Worlds. Pica, with an armor on, was defeated by Thousand Worlds, the force of which that Zoro can create is inferior to the force Jozu can create with Brilliant Punk because both techniques produce as much force as the user puts in strength, and Jozu has way more strength to put into it than Zoro has to offer. Therefore, taking an attack with Jozu's strength behind it with no Haki is better than being defeated by Zoro's attack with his inferior strength behind it(thus less force possible) while you yourself are covered with Haki.