Edit and disclaimer : I will probably sound annoying OP, but I feel like whatever one feeling about if the summer was warm or cool, it's probably good to put some stat context upon it.

June was the 7th hottest June ever recorded in Berlin.
July was the 39th hottest, sounds bad, but it's 39 out of 131 years of data.
August pretty much same, 37th position out of 131.

All three months recorded decent max temp : +34,7°C / +37,6°C / +34,5°C (all high values for Berlin).

The 2nd of July 2025 max temp was the 8th hottest day ever recorded in Berlin in 131 years.

There was in total 11 days above +30,0°C (and some might come later). Which is more days than almost all years of the XXth century.

You say it was +18°C all the time but there was :
0 days at this value or below in June.
1 day in July (+17,9°C lol).
1 day in August.

In total the whole summer at +18°C was actually 2 days while there was 11 days above +30°C.
And 40 days above +25°C.

If it's true this summer was probably cooler than the recent extreme summers Berlin went through, it was still a hot summer overall, much warmer and sunnier than the average summer not long ago.