First off there isn't a water pump in a dishwasher it's a sump pump water pumps are in cars. The door gaskets don't really do too much and every person that knows nothing about appliances thinks it's a super important feature, i get customers insisting on it so i gladly charge them extra for installation and do it and show them they paid for something that's doesn't do much lol. Only time a door gasket is really important is when you have a spray arm broken or stuck spraying water directly at the door then it may cause a leak but it isn't a common occurance. Most leaks i've seen on most dishwashers is from people not wanting to pay for it to be installed by a professional and do it themselves and don't level the unit from right to left and front to back. They usually install it to where it leans forward and that's what causes leaks alot of the time. Door gaskets i've seen good for 20-30 years. When changing door gaskets alot of times the aftermarket parts they create from china are usually way too big and causing door lock issues from the new gaskets being too thick and now not letting you close the door all the way. If you want to replace anything i'd change the door wipe/gasket at the base of the door that would be more affected if anything from better pressure but your unit may not carry it most models do. Now your sump pump gasket is mandatory if your tech tries to install a new sump without a new sump gasket you got a tech that doesn't know what he's doing.

He was right about replacing the copper line with a braided hose line we won't touch a machine that hasn't been upgraded because copper lines leak when you move them and work on the machines then the client wants a new floor or cabinets so if the machine has to move we won't touch it till it's upgraded. Well if he did lean on the door or it was bent that's between you and your repairman and yes a bent door can cause leaks. Sounds like possibly you're not dealing with a professional company they should of made you aware of that during the diagnosis but everyone's not perfect at spotting all your problems in machines some techs just get focused on the general complaint and sometimes overlook stuff. Oh and another aspect too for clean dishes with these newer units don't use these brands in your dishwashers or front loading washing machines (Kirkland from Costco, Sun, Purex, Arm and Hammer). Good luck.