so here is my take.
you was on LLU via ADSL24 (partial LLU)
you have moved to zen who are using a BT20CN service.
no BT FTTC planned for your cabinet or you direct to exchange. So no FTTC in forseeable future.
your speeds I think mrsaffron and the isp rep are probably right and you on a 2mbit IP profile. BT 20CN has a bad rep for stuck profiles, you may have to prod zen to get it unstuck.
LLU has various advantages over BT 20CN.
No IP profiles so your throughput should always be close to your sync speed.
Usually no DLM (depending on provider), so your line will not slow down due to temporary issues.
Cheaper backhaul meaning congestion less likely.