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I fear what he's going to throw at us next fight
(ttrpg.network)
To be fair, they did get some pretty decent damage in on their surprise round. They just didn't get many more chances.
If I were a player in this game I actually would be worried. The DM doesn't seem to have a clue how to make a balanced encounter and after this is likely to just look up random Monster Manual entries of a CR six levels higher than the party or throw so many weak ones at the party that the action economy makes it impossible to survive.
You comment does assume a bit of context. They might be a new DM just learning how to do stuff, in which case it's perfect fine to not be perfect every session.
Heck, it's perfectly fine to not be perfect even for experienced DMs. The most important thing is that whatever happens both the players and the DM learned something.
Getting an encounter perfect is pretty difficult to be fair, especially when the dice can completely wreck either side at whim.
A sneaky DM trick that can do a little better when reeling like that is "HERE COMES A NEW CHALLENGER" where the pushover battle has a slightly more difficult wave of reinforcements afterward, and maybe one more after that with some extra treasure incentive for it to be seen as a challenge rather than a punishment.