There is no comparison.
Today's grouts are far superior to the grout you see in pictures full of mold. Most grouts are acrylic based, however the acrylics used in grout are far more advanced than those used in the shower panels. To get a 3x5 panel of the same acrylic would be very expensive. A 3-foot x5-foot, 1" thick UV stabilized acrylic panel will cost upwards of $7000. This is why they are so thin and none are UV stabilized. This information that is available on any plastic manufacturer site or ask your AI to research it.
This, is why...
Acrylic panel showers can't be compared to tile showers.
They compare themselves to tile because tile is the gold standard and will continue to be long after the "cheap and fast" trend passes. The product they are selling has long been referred to as "glue ups" in the remodeling trade and have been used by weekend warriors and landlords for years as a fast and inexpensive solution to a bathroom that has seen better days. Instead of a full remodel that takes a week or more they can glue up these panels for about $300. Add a shower curtain or an inexpensive acrylic panel shower door and some paint and they can remodel the bathroom for under $1000.
The one-day glue ups run between $4000 and $12,000, depending on the accessories you select and the company you choose, so I have gathered some of the showers we have done in the $3000-$5000 range, so you can have a fair monetary comparison. There is no quality comparison.