Is this actually true for present time satellites? I find it hard to believe that teams designing satellites today would not go for such an 'easy' weight reduction, however limitted it might be.
Sure you can: one needn't test the full exact as-will-be deployed assembly to have confidence a system will work. Systems can be tested in parts or with surrogates.
Will the exact system in the exact conditions have been tried? No - but that's not really the goal; the goal of testing is only ever achieving an adequate[0] confidence of success in actual use.
[0] A situationally defined term.