This system is the best we can currently do with what we currently have. We resectorise the airspace so that we can get more through whilst being safe. There is a limit to what we can do whilst keeping you at your 'optimum' level.
The choice is that you put up with what is happening or you have longer on the ground with more delays as we have to regulate sectors to keep them safe.
On the West End at Swanwick, all the Heathrow inbounds through STU have to be at FL330 or below before the FIR boundary. Yes there were complaints to start with but we have to do that to meet the demand for the airspace by Dublin, Bristol, Cardiff, Cork, Knock, etc to get the level changes before the Sector 5 boundary without overloading Sectors 8 and 35
If you would like to complain about resctorisations, you can. NATS have to go though the ACP process. There is ample time to put you thoughts to the CAA. That said, I think that you'll find that most companies would rather be flying at lower levels and getting more utilisation out of their aircraft that just sitting at the holding point waiting for their slot.
Hope this helps!
CF