Ultimately, even without a single deck ADL fleet, there is still uniformality in the “new” fleet.
The interior will be the Lothian standard which for the majority of passengers is what is noticed - branding, seating, colour schemes, next stop information. The new vehicles are very much “Lothian standard” and from a technical point of view all the products are Volvos with common parts regardless of builder.
Issues arise when theres panel damage or configurations need to change however.
Then there's glass, advertising and passenger information systems. Each micro-fleet isnt exactly the same which means the parts store is rather varied.
A uniformed fleet of a product from a single manufacturer means every part can be used on every vehicle, even sometimes down to glass, which we only hold a very small stock of.
to be overly pedantic, it even goes down to cleaning and fuelling teams.
You have to train each team on where the AdBlue filler, fuel filler, screen washer and water fillers are, on multiple micro-fleets. The ideal is 1 uniformed fleet where everything is so similar that you can train an entire team on a singular vehicle, regardless of whether its double or single deck.
The idea before the previous managements departure (and Covid) was to sway more towards ADL and eventually only have 1 fleet type.