They’ve been able to blow up planets since the days of 9000 power levels, probably even with 1000, yet with power levels of 1B the fights are largely the same. Explain this as some sort of ki concentration, where your energy has…more energy per energy, or something?

To be a planet killer, you need a power level of around 2500. So 1000 is not sufficient, 9000 is overkill.

It's stupid if you think about it. Instead of fighting and potentially losing, you could just blow up the planet and killing every strong fighter on it because being able to breathe in space is not a learnable technique. It's kinda like the "why use any spell other than Avada Kedavra?" in Harry Potter and the answer is, there isn't really a point.

The Dragon Balls take a year to charge, but are often usable pretty much right away - the RR army get them 8 months after they were used, and despite being used to revive Goku the Earth balls are used basically a month later because Kami is revived. Maybe just explain it as Kami needing time to revive them as they’re intrinsically linked? It Kami goes on bed rest, you’ll have Dragon Balls in a few weeks…

The Dragon Balls source their power from the guardian that governs them. So, each set has different rules set by their guardian and the guardian can also arbitrarily change those rules. When Kami was revived, he apparently changed the 1-year recharge (if I remember right this is also said by him but I might be wrong, been I while since I've watched the early arcs). A definite change occurred when Dende took over guardianship over Earth and restored the Dragon Balls and made them about as powerful as the Namekian ones.

The biggest plot device in Dragon Ball are the zenkai boosts and how inconsistent they are in both power and occurrence. The one Goku got on Namek just prior to the Frieza fight was astronomical because they made Frieza way too strong even for SSJ Goku to defeat without an asinine boost. At the end of the regular Dragon Ball, Goku had all his limbs broken and a huge hole in his chest just above the heart, certainly a terminal condition, but he received no zenkai boost at all. When Radditz showed up, Goku was just as strong as in the 23rd Tenkaichi Budokai which makes absolutely zero sense. You cannot even pull the "it was just a showmatch"-card on that one because the finals were not a showmatch and Piccolo Jr fully intended to eradicate Goku to avenge his father.