Arguments to keep a firewall.

So, I'm trying to find reasons to keep a firewall in place at some locations right now, and seeing if anyone has an argument for it.

Right now we have a bunch of site locations that access some of our services. We run the network for thoses site and have generally a Fortigate firewall attached to a few PCs, or a Fortigate attached to a Cisco switch.

We don't have any advanced services running on these firewalls. They just have routes and policy rules. So, security-wise, all they're really doing is running an ACL for us.

We've been looking into setting up ISE and Trustsec for a little bit now. What I'm trying to do is figure out after that if we need a firewall in place if we have that. When it's only being used to ACL specific IPs and Services, and we can do a DACL to do the same thing with ISE.

Is there anything I might be missing that a firewall is giving us in this situation that would compromise our security if just using a Cisco 3750 with DACLs.