Here's just a few:
Losing Buu just for the sake of a lame comedy bit.
Having Buu in this saga wouldn't done three huge and much needed things for this tournament. A good writer would easily see the opportunities.
1.) Buu Could Bring Some Comic Relief.
Having Buu do stupid shit in the tournament would have been infinitely better than having him in a one off and highly predictable bit that eliminates his entire presents from the tournament. The reactions of all the U6 fighters after seeing Buu fight would be priceless.
2.) His Strange Powers Could Liven Up the Tournament.
Candy beams, broken regeneration, angry steam, and the attitude of a child. Buu would make for a great opponent for many U6 fighters. Imagine Frost going against him next, instead of Vegeta and discovering that he can't poison him thanks to Buu's gummy body.
3.) His presence could've helped with the power scaling.
Since Buu doesn't train, we more or less know his power level. He's somewhere between a Buu saga SSJ2 and SSJ3. Now if you put him against, say Frost, and he wrecks Frost then we know that Frost is weaker than SSJ3 and possibly SSJ2 thanks to Buu being a sort of measuring stick for us. As it stands, we don't know anything about anyone's power in this tournament. It's all guess work, but even the smartest, most observant among us can't call anything definitively thanks to the slipshod way this new series is patched together. Power levels aren't everything, but we should roughly know who measures up to who and in what way. We don't and that's a problem.
Not using ample chances to explain and show how Piccolo got so much stronger (if he did at all).
Okay, so Piccolo is now powerful enough to dodge Frost's attacks, tank many of his blows with very little damage, block his punches one handed while backstepping and charging an attack, and can bind him with one arm. Even being able to do this to a weakened opponent of this caliber is significant.
In the manga, it's worse from what I see. They fight on even ground, with Frost having taken even less damage from his fight with Goku and Piccolo still seemingly having an edge in their fight. To top it off, Piccolo's beam is strong enough to pierce Vado's godly barrier. So, if he's made these types of gains again, why not explain it? Why not have him train with Goku and Vegeta in the RoSaT? Why not have him train in the afterlife while he was dead? Why not have him give a random thowaway line, handwaving his boost? Why couldn't we even get that? Why is this show so damn badly written and poorly animated? I digress...dammit.
Anyways, we don't even have enough evidence to definitively know if Frost is stronger than base level Goku. We don't even know if base level Goku has god powers. There's evidence that he doesn't since Krillin could sense his and Frost's power. Then again Golden Frieza had regular ki too and was still stronger than both SSJGs.
Using normal Super Saiyan in the tournament without explaining how strong it is compared to Blue God.
Doesn't this just feel unnecessary and confusing for no reason? We already have no idea how much more powerful SSJGB makes Goku or Vegeta. Having them use the golden form to hold back just seems pointless right now, especially from a storytelling perspective. Toriyama and Toei seem to be keeping power growth vague, so I can't for the life of me figure out why they'd add this complication to the story. We've already established that the god level Saiyan's base powers are unbelievably strong since Goku dominated Final Form Frieza in base. That same Frieza that tortured a SSJ Gohan in his very first form. Having Goku and Vegeta use SSJ just muddies up what was already established with the base forms.
Now people are questioning if the base forms are even strong at all, now comparing them to Frieza arc characters. I don't fall into that camp but the horrendous power scaling gives them plenty of evidence. Obviously no one at Toei or even Toriyama himself cares about making this show make sense any more. Having at least a vague sense of how characters compare to one another would be nice. Horrid power scaling makes this impossible though.
Other Notable Mentions:
-Not explaining Vegeta's rage boost.
-Not using the red haired God form again
-Not showing Frieza's training (shooting Togoma over and over again doesn't count)
-Not showing more of Piccolo and Gohan's training or showing how strong they got.