I would not agree completely To put it simply, it mostly depends on the price of the device.
Most people buy the cheaper ones, starting them up can takes up to 3-4 minutes (!).
And even those that are under constant power can be turned off completely. Actually, the part that starts the android, while some other modules can continue to work (clock )
In addition, in order to set which applications should continue to run in the background, you need to carefully adjust Android policies. Exactly the same as with mobile phones.