If you mean that armors and outfits will look like they are jury-rigged together from scrap materials in the post-apocalyptic world then yes, the art style shift will be very much like how the guns started out looking like regular modern day weaponry but then turned into guns that look like they were put together in a post apocalyptic world by working with whatever junk was at hand. Same with the workstations and same with the landclaim block and same with more things so that eventually you won't be able to say that the guns look out of place any longer. They will conform to the same art-style being used across the board. Breath of fresh air seeing as there's already a bunch of games you listed that seem to copy the same "classic" art style for a zombie themed game.
Breath of fresh air you can say about Blight. Usualy games set in Medieval are fantasy - you know magic etc. while blight is going into sci fi ( The last of us fungus like) which is fresh air, XIV century west europe aesthetic + zombies. Armors, Weapons etc in this same period.
okay at first let's take Mad Max as example ( just game it will be simpler ) : this game artystyle is consistent.
place is seaside near nuked sea. So - water evaporated so there was a lot of salt in air : so this caused rusting things + sand so covered building it collapsed. so hard to find things because a) most of them is rusted b) under sand yet in bad condition because of.. sand. Old people like Max behave like prewar ( clothes etc) while "post war" borned people do random things because they don't know how it was working. In Mad Max there is lack of guns or even clothes thanks to salt and sand. So using junk there is suitable because... everything else rusted - workling V6 engine is treat there as almost saint relict. Bandits wear normal clothes while "civilians" literaly rags. So there is totaly nothing and nothing to go because are cut off because of radiation zone - just sand and totaly nothing else - happens maybe 20 years since nuclear war + lack of weapons can be caused that's Australia not USA
Walking dead - classic zombie art style. i don't have to explain.
L4D2 - outbreak period srtyle
7DTD - totaly lack of consistents
Armors and guns are like Mad Max - made with totaly junk or using part of junk- looks like nuclear war happend 300 years ago if there are living trees ( so zone wasn't destroyed) yet guns somehow manage to be totaly destroyed ( well still is in the use are pre ww2 artilery ammunition in our world so i think i secret bunker should have +- 1 000 guns at least : so even if it was long time looted then... there shoudn't be infected too + this is USA not Australia. ).
World - you can find realy good condition miltiary trucks, electricity is working, vending machines too so situation about world is even closer to l4d2 that even walking dead - looks like this bombs was thrown month or week ago not 10 years ago. So if there still exist such thing and are good condition that mean that rest of stuff should be too.
So all of this games ar: to be consistent there is two options
a)
7DTD go "classic" way - days gone, nmrih2 etc. - mostly civilian clothes, armors are fabric - swat, army, firefighters, maybe a little bit rusted but "standard" weapons with standard attachments - ak , m16, scar
B) go totaly in mad max post apo - remove all cars, most of map is sand or burning ruins, forests are realy realy realy rare, almost no electricity, zombie go almost without clothes ( you know if civilians clothes doesn't manage to survive in city center then wound't survive on zombies either), 90% of POI should be change into almost destroyed ruins ( wasteland biom almost everywhere) ,
Because now it's not consistent at all