Yes that is my frustration but I also question the idea that every serve that isn't hit big will be destroyed. I have seen too many returns blasted long or into the net to believe that a slow serve means instant point loss.This. I totally get how OP could be frustrated. Big flat serve that never goes in and that is followed by hard slice that is not very reliable.. IMHO try to have your partner hit two slice serves to boost up his percentages. This can work - I have seen several 4.0 and under guys hit nothing but slice one hard and one softer and still not double fault often.
Most lower level player simply don't have a 100% reliable serve people can't tee off on. The issue is this - a kick serve reduces your serve speed by at least 20mph. So if you hit a 70 mph first that means your "kick" is like 50MPH.. Hit a slice second serve with a bit of top - and you can still hit a serve thats not an easy crush.
In the same way amateur players don't have 100% reliable serves, they don't have 100% reliable returns either.