The old action scene wasn't terrible (I've seen worse in pretty big webcomics), but it was unfocused, with a slightly janky sense of the momentum, and the relationship between cause and effect, the attack and the reaction, making it feel unfocused, and the space in panels wasn't used quite efficiently, so it felt just a little amateurish (even though the actual drawing of figures, perspective etc. wasn't bad).
The new one looks excellent. You could put that in a portfolio to show a big print publisher and they'd likely be impressed, because that's publishable quality work. There's a strong sense of momentum, I can tell exactly what's happening and what the impact of the attacks and the reactions are, and the choice of shot angles are dynamic and use the space well.
In summary, great job, you should feel proud of yourself. 