Practice is just that it’s practice. It’s the best way to try out different weapons without actually being in combat .
Army is always trying to make training as realistic as possible, but nothing is as realistic as actually being in battle. So all things being equal the practice range shows us det packs are more effective at killing tanks than the current bomber AT weapons.
How would making them available earlier make them better? Just increase AT efficiency against tanks and decrease throwing range of tnt.
Yes as stated in the OP, the AT pen for bombers should increase and the Armor models needs to be fixed along with decreasing det pack effectiveness against tanks need to be decreased.
But after all this is done bombers should be available earlier in the campaign to make sure that tanks don’t run all over the battlefield unchecked in the early campaign …
Perhaps unlocking bombers before unlocking tanks could be an idea. Have bombers unlocked by default and have tanks come later (planes even later).