In the last two weeks I've had 70 people sign up through a web form, but only 5 ended up on my list because they completed the double opt-in.
Is this normal..?
No, it’s not normal. Based on my experience around 10-20% of subscribers don’t verify their email address. You might have a deliverability problem so you’d better contact your email marketing provider.
That seems very low to me. Usually, only ~25% don't double opt-in for my site. Is there a problem delivering those emails? Maybe when they signup you could nudge them to double opt-in after they recieve that email?
I have 140 subscribers and around 35 who are on pending list. I am using Email Octopus which allow me to see pending emails too. If it is on poending for too long (> 1 week), I manually send them an email and ask do you want to join. Got around 10 confirmation using this method.
I have no data. But double opt-in is likely a requirement of most privacy and antispam regulations all over the world, so I wouldn't feel comfortable not enabling it.