Your previous bag was probably only rated water resistant if it had a zipper (like biking in the occasional rain), not waterproof (like having a bucket of water dropped on top of it) so having a hole for the bladder tube was acceptable. Before your zipper failed, would you have felt safe if that bag fell in the lake with your laptop in it? Would you have felt comfortable stand up paddle boarding all day with your old bag when you could easily fall in? This bag is designed more for water sports than say hiking or biking. Perfect for leaving on a wet coach boat while sailing off wet & windy Sandringham and then walking home afterwards.
Top loading roll top bags when properly seam sealed are designed for that, very common in river rafting. Bags with zippers are not (at least 99.99% of them), zippers are not waterproof except for very large, heavy and expensive ones used for dry suits (as an example). The outside compartment on this bag with the zipper is stated as only water resistant.
Unless the bag has an additional outside sleeve for a bladder thats seam sealed from the bags main compartment then it's not waterproof. Even then these type of bags are not completely waterproof without expensive materials and with professional and thorough assembly & testing. Cheap asian bags need not apply. There's many levels of waterproof as most companies liberally and loosely abuse the term waterproof like they did with wrist watches. It sounds way better than just water resistant.
I hope this helps explain.