rahel - more context is needed, since the term can mean a lot of different things in different surroundings

die Anlagenkapazität war zu gering bemessen

"inadequately assessed" might work

in this case you can simplify to:

the machine (if Anlage is a machine) or factory ( if Anlage is a factory ) is too small -

Anlagekapazität sounds like it's been blown up from something which is simpler.

if you want to keep the more complicated words, then:

the machine capacity was underdimensioned