I still don't think Max Concentrated Shot and Max Burning Land are the best for stages.
As people have already mentioned, the damage from max Concentrated Shot is mediocre. If you want to keep it for stalling/flinching, then leave it at 1. Burning Land at least does a lot of damage, but it leaves you very vulnerable against unflinchable bosses. The skill isn't cancellable at any point, and there's even some delay at the end. Against unflinchable bosses that can hit you at any time they want to, Burning Land is a risky skill to use. You could argue that the smart thing to do is to freeze the boss to give time for Burning Land, but there are better attacks to use after freezing, such as Iron Bomb or Impartial Shot. I understand that maybe it's not that much of a big deal since we're dealing with horrible and slow stage AI, but that still doesn't change my stance that Concentrated Shot and Burning Land are not the best skills to use.
I'd recommend either maxing Magma Explosion or Flame Impact, because they both deal more damage than Concentrated Shot in a shorter amount of time. Both of these Grenade skills also are dash cancellable, with Magma Explosion being easily comboable and Flame Impact being a hard knockdown.
I'd recommend maxing the Physical Damage passive, but its effectiveness solely depends on your ability to >>AS S consistently and in rapid succession, which not many players have mastered (or even plan to master).