It's easy to make a waterproof jacket that weighs less than 7 oz. However it is very hard to make one that waterproof and breathable and lightweight. The lightest Event rain jackets come in at 9 to 11oz which is about double the weight.
Today most people don't want a just waterproof jacket. Instead they want one that is breathable and waterproof. So when a gear manufactures is selecting a fabric for a new rain jacket They have a choice of a really good fabric like neoshell, Event, and Gortex. But these fabrics are heavy and costly. So if you want to target the light low cost market the good fabrics are out leaving the manufacture with a selection of polyurethane Waterproof breathable fabrics.
Polyurethane is a vapor permeable membrane not air permeable. As consequence of this breathability rating of polyurethane is mainly determined by how thick it is. Thick is more durable but less Breathable. Thinner make it more breathable and less durable. Most polyurethane WPB fabrics are however cheap and lightweight.
But the manufactures don't talk about the limitation of Polyurethane and it wouldn't surprise me if most gear manufactures are also unaware of it. Polyurethane works best when the humidity inside the jacket is high. The amount of moisture that moves through the fabric is very low in dry air and reaches a maximum at about at at least 80% humidity. Most people are comfortable at a humidity of 50% or less where polyurethane doesn't work well At humidity over 50% most people people feel damp and start to open vents in the jacket.
So in the end you have a jacket that does appeal to people because it is light and not that expensive when compared to Gortex, Event, or Neoshell. However the final product is also less durable and less breathable. Now a manufacturer can compensate for this by offering a warranty and raising purchase price to cover the warranty costs.
So when other report it's not durable and doesn't breath well, I am not surprised.