Another dumb decision made by openreach, not to allow people to change to fastpath or interleaving.
Being part of DLM is not on.
Yet again, you are making sweeping assertions based on how you want the world to be, rather than listening to the many here who speak based on understanding of the technical limitations.
You started a long thread about 'fibre speeds should be fixed', and it was explained to you several times that if you wanted a fixed speed FTTC product, it would be provisioned on a huge noise margin to allow for the inevitable fluctuations in VDSL line conditions and would still likely need a "it's too hard - we give up and release you from your contract" clause. The huge noise margin means you would lose a substantial proportion of the speed the line is capable of. I covered this in more detail
here.
Consumers tend to demand the highest 'up to' figure that works - which is where DLM comes in. Generally, it seems that BT Openreach's FTTC DLM works fairly well, though it is arguably a little too persistent in holding on to restrictions after line conditions improve and their necessity has passed. It is also nonsense that, at the moment, it sometimes takes an engineer visit to remove an unnecessary banding. I'm sure BT Openreach will improve these things in time as they continue to refine the FTTC service in the light of operational experience. Hopefully vectoring will be deployed as part of these refinements over the next year or so, which will help to ensure all lines perform to their full potential.
VDSL2 allows for modest levels of interleaving and impulse noise protection, which have a small effect on latency - much less than on ADSL2+ - but potentially a dramatic effect on stability and performance. As such, BT Openreach have refused to give Customer Parties 'fast path or bust' setting on FTTC - it's better to give DLM access to a full range of strategies.
If the FTTC DLM can leave a line on fast path, it does. If interleaving is required, it is set - but it is eventually removed if it is no longer necessary. It seems that the FTTC DLM initially opts for modest levels of interleaving and/or INP rather than resorting to an increased noise margin with the consequent drop in sync speed. This is in line with what most consumers will want - they would rather keep speed at the expense of a modest increase in latency and jitter. The only setting Customer Parties have on BT FTTC line is a choice of three different DLM trade-offs between speed and stability.
Twisted pairs will always be limited by the physics. If your require the low latency and jitter of fast path, guaranteed line speed (but not necessarily guaranteed throughput in the absence of an expensive service that guarantees throughput - I guess we will eventually see an Etherway over FTTP product) and a migration path to higher speeds in the future, FTTP On Demand will be available to those in FTTC served areas later this year. It will not be cheap, however.