It is what it is......a day bag 25ltrs............. so I doubt it will be rammed with kit......so is the weight of the bag really that critical?
Ramming kit in there would make for an uncomfortable carry.
Putting a piece of thin ply in the back would keep it square on the carriers back and may offer better comfort.
Dimensions of the ruck sack:
54 x 30 x 20 cm
Dimensions of the folded german army sleeping mat:
38 x 27,5 x 3 cm
That means the german folding mat fits perfectly in the Swedish rucksack next to the back.
The mat weights 425g and costs used 10 €.
Water will enter through the zippers and in the end they will break and you will get a problem, if that doesn't happen in town.
That's a city bag.
Your's I don't know.
But that happens to all, that look like yours.
Sooner or later depending on the quality.
Of course you can buy for your money what you like.
But if you ask us, before you buy something, what we think about, we could help you to avoid wasting money.
90% of the stuff on the market you can't use for trekking tours, and only 10% will last longer than 5 years. 3% longer than 10 years.
We know, what lasts a lifetime.
And the prices are very similar.