Fresh Tomato does have VLAN support in GUI though and what Asus calls AiMesh can be re-created on 2x RT-AC68U routers plus extra features AiMesh doesn't have in original firmware for this model. Someone on a budget with no big performance needs or expectations can actually do it.
The point of AiMesh is centralized management. Having a bunch of APs and Repeaters doest not re-create that.
The main purpose of a mesh network—including AiMesh—is to extend your Wi-Fi’s range and allow clients to roam reliably between nodes though features like "Client steering" and "Band steering". Simply setting up access points with the same SSID does not achieve this in my experience, as clients tend to perform poorly when switching from one node to another as the signal weakens and a stronger one becomes available. This has been my daily experience with an iPhone, as well as other clients.A bunch of VLAN capable APs with individual channel and power output control is better than central management with limited control and all "nodes" sharing the same channel available bandwidth. It doesn't re-create AiMesh drawbacks either.