Can you create your own inventory/ condition report that details what state it was in when you moved in, room by room, so that it's clear that you don't necessarily agree with whatever their version said?
(if you have any evidence/ photos taken at the time, that would bolster your case)
Landlords are supposed to budget for what is considered "fair wear and tear"!
This means the kind of issues that you'd normally deal with in any house, however careful the residents are, because they're an entirely normal thing that happens over time. It's so normal that HMRC allow landlords to claim these as costs entailed in running their business.
As well as worn out carpeting, the list includes things like occasional scuff marks on walls, doors, skirting boards and hard flooring; (such as settlement cracks in plaster; chipped and faded or slightly discoloured paintwork; loose cupboard handles and hinges; worn kitchen counter-tops; warped blinds and faded curtains...
Decent landlords and housing providers would have a maintenance schedule, and also replace things like kitchens/ bathrooms after a certain number of years, and also regularly check the condition of roofs, external walls, drainpipes, window frames.
There's a legal requirement to check things like smoke/ carbon monoxide alarms, gas boilers, electrical wiring etc at set times, but apart from that, a failure to carry out any inspections, proactive maintenance or repairs throughout the length of a tenancy would count against them if they tried to withhold your deposit.
PS: Just went and checked. According to some websites there is guidance for landlords about how to calculate the cost of any damage, as they're supposed to take depreciation into account and not profit from what's called "betterment". This details what is officially considered a reasonable 'lifespan' for various items - eg a washing machine is meant to last up to 6 years, a hallway or staircase will need redecorated after 3 years. One table I saw says that one would expect to replace a "budget carpet" after 3 years, a "medium quality" one after 8 years, and a "top quality" one after 15 years.