I am not an expert here but it seems dangerous to assume as you do that the baseline of “correct number of ventilators” is the UK number. They could be...

-Under provisioning for surges (not even Covid, even just a sudden emergency of another sort, a bad flu season, big accident, terror event, whatever)

-Going longer between maintenance intervals than is recommended

-Delaying ICU admission longer than is strictly recommended

-Relocating ICU equipment as needed more than other countries feel comfortable doing

-Using more reliable ICU equipment (does the German figure include any older and potentially less reliable gear in the former communist east?)

-Have less need among population for ICU

On the last point, Germany has accepted by far more refugees from MENA war zones than any other European country and I would not be surprised if this resulted in higher emergency medicine use.

Also a quick Google shows Germany is a bit older with 22% of the population over 65 vs 18% in UK.

None of this is to say Germany isn’t over provisioned but it is probably not 5X over provisioned, if it is.

At some point under-provisioning is no longer an efficiency miss but a national security issue of how clogged your infrastructure gets during stress.

Maybe that they count them as beds and have more that can cater for ICU than others.

However, let's not forget historical factors and was case of many countries having armies in Germany for legacy war reasons and that may well of seen the mentalities to have a higher number of such beds than most places.