Overhealing is definitely a bad thing, admittedly I did it a bit in my first A1s run (yesterday) but only because I knew I was with a skilled and experienced group.

Back in the early days of A4n, I had a co-healer tell me that my HPS was "Ok". They were the type to get Med II up the whole run and aggro all the adds and spam heals, I had a good laugh and never ran with them again.