I seriously doubt that a powder like Persil or Persil colour is particularly damaging to fabrics, in fact, I find it quite gentle and all of my clothes come out nice, soft and fluffy
I have noticed no damage to fabrics, no stiff fabrics, no precipitates, no problems generally at all and it rinses out very easily and smells nice and mild.
If I add a softener, like Comfort pure, I get even softer results again.
It's not that my clothes are filthy dirty when they go into the machine, far from it but I do have some stains to cope with that I found many of the liquids failed to perform as well on.
You don't have to be a mechanic or, living on a farm to get these either.
Problems I face regularly:
1) Tomato sauce stains - from pasta sauces etc
2) Stains from highly staining indian food
3) Tea and coffee stains
4) Sports gear - grass stains, mud etc
5) Oil (cooking splashes mostly olive oil) or salad dressings
6) Marks on collars of shirts
Then if you add things like tea towels and table cloths -
Pretty much any food stain you can think of!
Unilever Persil (including the colour version) will remove all of those, without any quibble on a normal wash. No pre-treating, no messing around. Just put clothes into the wash, half scoop of Persil and and no risk of any problems.
Ariel performs equally well and I'm sure Henkel Persil, Le Chat etc is outstanding too.
If a detergent can't handle the above without any fuss, I really don't see the point in it.
I find in general with liquids that they are just mediocre performers. I have found them particular poor at dealing with oily stains from things like salad dressing / accidental splashes.
Also, the powders, both Ariel and Persil are vastly better performers in QuickWash programmes - there's no issue with them not being dissolved even in that short a time.
The only advantage I could see for liquids in the US is the fact that some people like to wash in cold water which may make powders tougher to dissolve up fully.
Once the water's 30C + it seems to work fine for the TOL brands on this side of the atlantic anyway!