Thats a good point, the numbers migrating potentially will become so huge even a country with the most sympathetic and funded migration policy will struggle to deal with it. Trying to stop people coming through unregulated ways and through proper channels is good but on its own wont make any difference in terms of the system being overwhelmed.
The answer is to really start to focus on creating stability, safety and work in the countries where people feel they have no other choice but to leave. That means directing money, resources and clear plans and policy with those countries. It needs to be done at a UN, EU,UK level.
With so many green and sustainble projects required throughout the world and in every country, any idea theres not enough work available for people is a lie.