It can be very serious, yes. For most, it's not, and anti-vaxxers seem to consider their own lived experiences to be better evidence than stats like "thousands die from flu every year".

I have a medically sensitive daughter and the folks who go "flu's not that bad, just get it and move on" drive me insane.

I hear you... I've been blessed with multiple recurrences of shingles within six months of one another. I'm one of the lucky recipients of that rarity.

"somewhat true" implies not entirely true. Iv'e had chicken pox. It wasn't serious, but as you point out, that's not the whole picture.