Configure routing polices based on source IP address

You should be able to and from what I read, it can be done like the way it is done on an AR platform, at least  my AC seems to support these commands and the AC series oficialy support PBR.

So you might want to try :

https://support.huawei.com/enterprise/en/doc/EDOC0100585934/ccc21e9/example-for-configuring-interface-pbr

But to be honest I would not burden an AC with a whole lot of L3 functions, it is a capable platform for sure but it is not really intended for L3 features, for instance there is no vpn-instance / VRF  support on AC's.

So why not stretching the vlans to their end device ? If there is L3 in between i would use vpn instances to separate.

PBR is nive when you need it but usually is needed to try to sort out IP design flaws which makes such a problem only bigger bij the added complexity.

Do realise that reading a routing table is not sufficient anymore to understand forwarding behaviour.