Glad to see you came around.
I'd fully agree that, for their original manga and anime, Dragon Ball > One Piece for a few reasons. The most prominent would be character writing. One Piece has characters that had interesting premises or backstory, but its need to have them remain recognisable ends up severely limiting character development and growth with most of the main cast becoming one-note after Alabasta (aside from during the Summit War Arc, and even those changes to the typical narrative were only temporary). Luffy is dumb outside of battle and happy go lucky despite the story calling for him to take things more seriously, Nami's obsession with money remains one-note even after it was given meaning and resolved in Arlong Park, Sanji's simply been given unbelievable disrespect as of the timeskip in general and it's impossible for the gag of Brook wanting to see Nami's panties to be funny when it's repeated 50 or so times. Meanwhile, there was a clear sense of growth and development amongst each member of the main cast throughout most of the arcs. Goku, Vegeta, Piccolo, Kuririn, Tenshinhan, etc. were all completely different in many aspects by the end of the series compared to the start (Piccolo literally being a completely different person in general) and the addition of new generations helped further this with aspects such as Goku's fatherhood in the Cell Arc, how family changed Vegeta by the time of the Boo Arc, etc.
The second reason would be arc structure and identity. It's easy to write off DB's arcs as simply being "fight bad guy -> power up -> win" but that strawman has no weight behind it when there was quite a variation in how each arc played out such as the Hunt for the Dragon Balls or the Red Ribbon Army Arc being completely different from the more battle-oriented arcs, each of the tournament arcs having their own identity or the mainly battle arcs that comprise the entirety of Z (Saiyan Arc presenting a major tonal shift for the series as it went from fantasy to sci-fi, Freeza Arc adding to this whilst having a more complex quest for the Dragon Balls than prior with 3 main factions, Cell Arc having themes of family throughout its later portions as well as the flaws of the main cast being given physical form with Cell and the Boo Arc bringing the series back to its roots somewhat with a comedic tone and magical, fantastical elements). One Piece had variation in some of its arcs, but most of the New World arcs have just been poor man's versions of pre-timeskip events and the series has come to follow a predictable formula in its arcs of exploration -> rescue -> main conflict, combined with how limited Oda's scope of executing his themes are with how repetitive the "you're my nakama!" line gets.
Thirdly would be in the different approaches to planning in general. Whilst I'm a supporter of authors planning each detail out before writing over improvising, Oda only really does this halfway and it really starts to show after the timeskip. This provides modern One Piece with a similar problem to what Super has with Beerus' power compared to Goku and Vegeta with it setting a ceiling yet struggling to work within those limits for power and abilities. For example, things such as Luffy beating a Shichibukai like Crocodile so early (something Oda has even said he regrets having done) despite how minuscule even the strongest version of pre-timeskip Luffy is compared to New World characters really damages the reputation of the Shichibukai being meant to be one of the three great powers if this was so early into the story and so low on the power scale. The same goes for how much reverence Kuma and Moria seemed to have for Lucci and Luffy's feat of beating him despite how irrelevant the latter would be shown to be at Marineford, forcing Oda to introduce elements such as CP0 to make up for this. Perhaps the biggest case of Oda planning out far less than he let on is how at the supposed war of the best that was Marineford, none of these top tier fighters showcase the physical signs of Busoshoku Haki or seem to use it much if at all despite it being an arc where all their great abilities were meant to be on full display, yet every character worth a damn in the New World starts showing such physical signs of blackened limbs and the like when using it after the timeskip. There's then of course Luffy hiding Gear 4th until Dressrosa even when having to destroy the Noah where it would've been incredibly useful, yet uses it so liberally after the Doflamingo fight. Despite DB suffering from such power creep as well as some continuity issues, few of them were as apparent as many that OP has done for the past decade and at least didn't place a limit on itself that made later escalations less believable.
This extends into another problem with One Piece in its over-reliance on mystery and building up later events over actually executing them. For example, the only real positives in the Skypiea Arc come from what it'll set up for later events rather than what actually happened within it or how Oda introduces so many mysteries that he's dead-set on keeping all for the final arc rather than naturally revealing them naturally when called for. For instance, that reveal at the Reverie would have been the perfect moment to reveal at one of the great mysteries, yet all it added was more questions and no answers. The problem with extending a mystery out for so long is that it hypes it up to the point of having expectations that are unrealistic to fulfil. No matter what the One Piece, Will of D., True History, etc. all are or how they interconnect, there's no way they can live up to the wait with what's come between it ranging from meandering to damaging the endgame.
That's without going into full detail on what makes the timeskip arcs in general so riddled with flaws even GT's quality is arguably better, but that's an essay for another time.
In short, One Piece had the potential to be as good or better than DB, but several aspects such as character writing, story structure and how its overall length harmed these rather than helped stopped it from reaching its full potential, with DB's heights arguably being more solid and its lows not being as low as what OP has reached (especially the Wano Arc). Things may have been different had Oda stuck to something close to his initial draft and restructured the story into one that ran for 5-10 years, but wondering what might have been is fairly pointless right now.
