More or less this.

I see a certain version of this at 2/5nl. There are a ton of 2/5nl players who can't beat 1/2nl and 1/3nl and likewise have problems with "certain" 2/5nl players.

these players have an inflexible style of poker that only does well at a certain table and it just so happens that 2/5nl has more of those tables that their style works best at. However, simply add one or two "donks" to the table and all of a sudden said players become horrific losers because they can't adjust.

I know a 2/5nl player who is an absolute beast when he is at a table he is running. When he's the only aggro thinking player at the table, he will easily chip up 300BB, 400BB, even 500BB... But if you put just one other decent thinking player at the table, he becomes a horrific loser. And the reason is, he only has one gear and just doesn't adjust well...

I think the most imperative question to OP is...

How many hands of 5nl and 25nl have you played? As pointed out by someone above, it's likely a sample size issue. What javi/dgi said may be true, but we have to clear up the former part first

Very true.

When the deck is smacking you in the face, nothing in the world is easier than poker.

I remember when "he who shall not be named" started a PG&C thread playing the micros. His play was attrocious and he was getting killed at 2NL and 5NL but then he jumped up to 10NL and for the first 2 days he was just killing it until his heater ran out of luck-juice and he burned through the rest of his roll in less than a week...

so yeah, sample size is definitely the big pole in the tent...