They have low stats on attack. I am open to as many answers as possible.
100% Yes! Blissey and Chansey are the #1 and #2 special walls, respectively. They may lack in their attacking power, but their special walling capabilities are amazing. If you get the chance to get one, It is well worth it to train.
Yup. They are. Just because they have low attack stats doesn't mean there no good. The opponent can spend hours trying to knock out chansey while chansey is paralysin' pokemon. As long as you have a chansey or blissey that will make YOU happy, that will answer your question.