Disadvantages of functional testing
I have read that functional testing is not that suitable when there is a lot of interrelated inputs. Is my understanding correct that e.g. following program would be really difficult to test using functional testing (test cases):  
`Car configurator with e.g. 20 fields, each of 20 choices, giving 400 possible 
 combinations.` 

I would say no one would write 400 test cases for that. But while this is still testing its functionality, we still call it functional testing, correct? But isnt it actually risk-based approach when only some combinations are tested?
Disadvantages of functional testing
===

I have read that functional testing is not that suitable when there is a lot of interrelated inputs. Is my understanding correct that e.g. following program would be really difficult to test using functional testing (test cases):  
`Car configurator with e.g. 20 fields, each of 20 choices, giving 400 possible 
 combinations.` 

I would say no one would write 400 test cases for that. But while this is still testing its functionality, we still call it functional testing, correct? But isnt it actually risk-based approach when only some combinations are tested?