Just because its not integrated doesn't mean its replaceable. Some companies only are replaceable with that single part. Looks at asus, tons of non dedicated gpus but they use a proprietary connector most of the time.
i have a great laptop cooler. it has two massive fans. i feel like there's no way this laptop isn't getting enough cooling!
Fans don't mean much of anything. If the heatsinks are clogged you could have a box fan inside your laptop and it would still overheat. Think of it this way, airflow (fans) is cooling potential, efficiency is determined by how well the heat sink transfers heat away from the chip and into the air.