New Mixer Tap - very low pressure

If your apartment does not have a pump or is not pressurised then you could have a problem with some mixer taps , you could get a tap suitable for low pressure but will never be as good as the previous taps you had

You would know if you have a pump as you would hear it running when you use a tap or shower , if you have a storage tank in your attic ( if you have one ) as you said your on top floor , you probably don't have a pump , its hard to say what's involved in fitting a pump if wanted without seeing the layout of your apartment , but chances are everything would end up getting pumped , which would mean whenever you flush a toilet the pump would run until the toilet refills which can be annoying in the middle of the night .

Ok if you have a mira vigour fitted then you don't have a pump in your apartment.
I would double check with your plumber that the taps he fitted are in fact suitable for low pressure systems , but even ones for low pressure are pathetically poor for pressure , so I would have to say yes it is probably going to be as good as your going to get , your plumber should have explained this to you before fitting them , I always mention these things to a customer before fitting them as it gives them a chance to change their minds , its the same with most ballvalves that come with modern fancy toilets , they are generally not suitable for gravity pressure they take forever to refill the cistern after flushing .

If the plumber supplied the tap then he is wrong. Its not fit for the purpose. However if you bought the tap and he fitted it then its up to you to replace it.

Tbh if the plumber was professional he would have checked the pressure on the tap.