> In nuclear war, practically all detonations would be airbursts. They don't cause similar fallout.
No, definitely not. It really depends strongly on who your opponent is and what their strategy might be. And on whether they stick to their pre-anounced strategy. And how many exchanges (first, second, third strike) you might get to.
Generally, there are two strategies that are usually distinguished in US literature for leading a strategic (i.e. big, as opposed to small, tactical) nuclear war: counter-force and counter-value.
Counter-value means that your nukes target what values the enemy has by destroying enemy cities and the population and goods/industry/infrastructure in those cities. Destroying a large, non-reinforced, "soft" target like a city with humans in it is more efficiently done by airburst, because the overpressure/temperature effect is weaker but spread over a far larger area. Weapons also don't need to be that accurate, if you miss downtown Manhattan by a kilometer, it won't matter much. Most smaller nuclear powers, those with a no-first-use doctrine and those without accurate fast delivery systems (i.e. modern ICBMs or SLBMs) do rely on a counter-value strategy. The goal there is usually something akin to France: They aim to be able to kill more of the enemy population than there are French to kill.
Counter-force means that your nukes target the enemy military infrastructure, most prominently ICBM silos and command infrastructure. Usually this strategy calls for a preventative first strike with very accurate weapons that can destroy heavily reinforced underground structures surrounded by possible anti-missile systems. Meaning you have to hit the target with multiple ground bursts, quickly and as accurately as possible. Since you have only one try at this, some of your warheads might be shot down and some might miss by a few hundred meters, causing the crater to not destroy that ICBM bunker enough, there will be quite a few warheads on the way to each single silo. Meaning that this supposedly "humane" strategy will produce enough fallout to still kill a lot of the enemies population. One example would be https://www.nukestrat.com/china/Book-173-196.pdf p184, where a US counter-force strike against a Chinese missile silo site out in the sticks would kill between 5 and 20 million Chinese just from fallout. And of course, if your counter-force strategy includes command bunkers near capital cities (ground burst), nuclear submarine bases near other harbors (ground/sea burst) or larger military airports (air burst), you are bombing much closer population centers, also with mostly ground bursts. Most prominent in claiming a counter-force strategy is the US.
So most probably, if your opponent is the US, GB or Russia, you'll receive a large number of ground bursts in the first strike. Only if there still were an exchange after that, would there be any significant number of air bursts.