I'm more inclined to go with
@swifty's view that it might be to do with their use on country work such as various Mendip Explorer or the D1x routes where their extra length may be an issue. Certainly, the similar aged ones on Bristol P&R look in much better nick. I don't know if the colour matching is poor on the Bath ones or if the paint fades quicker than the factory baked examples but they look a right mess.
These are typical (credit to photographers)
First Bus West of England 'Bath Unibus' Enviro 400MMC YX66 WEV 33946 + YX66 WFA 33948 , Weston Island Depot Bath 16.2.20
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Explore Mendip Bus' 1000 photos on Flickr!
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Explore Mendip Bus' 1000 photos on Flickr!
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On 33947, you can see the obvious panel minus the logo but the n/s corner has also clearly been, and think the o/s and panel beneath the cab window are also replacements. 33948 is even more glaring.
The 65 plate ones don't look too bad but there is the odd scuff etc