Thanks for your response and your constructive criticism. You’re absolutely right.
The solution you choose all depends on what your priority is concerning the use of the firewall. If the firewall is used just as a filter for the edge of your network and you don’t require inter-subnet filtering (generally the case on smaller networks), then you could alleviate the ASA from the routing functionality by routing within the network rather than on the ASA edge. Also, the question (from my understanding) dealt not with datacentres, servers etc, but end users on distribution switches. Of course servers would be placed in a DMZ allowing filtering between end users and servers but this was not mentioned in the solution. I should have been clearer.
On larger networks, where inter-subnet filtering even between user groups is necessary, and ISO compliance is required, then yes, multiple DMZs and internal should be implemented with multiple subnets and some routing should be implemented by the firewall. However, the most intensive routing should still be taken care of by layer 3 core switches/routers and not the ASA. This can be seen in Cisco’s Enterprise Internet Edge documentation and recommendations.
Ultimately, the point of my post was to state that Cisco’s best practices indicate that the ASA should not be used for the bulk of routing. This should be done by the core layer (or the collapsed distribution/core layer in a 2-tier hierarchy) and not by the ASA. Because however I am not familiar with ISO requirements, if they are stricter than those of Cisco, then by all means, they should be implemented if they are required.
Thanks again for your valuable input.