Yes he could buy a cheap bike, but he isn’t buying access to a single cheap bike. They are getting access to a network of 1,000s of e-bikes and scooters, placed conveniently throughout the city, maintained by professionals, charged by someone else, with 0 theft risk. You don’t have to think it’s a good deal for you, in order for it to be a good deal for them. If you want a durable, maintained, always charged e-bike, with insurance so you don’t have to worry about theft you are going to be spending a lot more than £300. I used to commute by bike, and a shitty bike makes for a shitty commute, especially in a place with weather like London.

You could save even more money by not buying a bike and just running everywhere. Do it barefoot for additional savings on shoes. Some people might call that “insane”, like you calling £1.50 for an e-bike rental “insane”

You don’t think the value is there, and that’s fine. I’m just pointing out that lots of people don’t think that amount of money for years of transit service is unreasonable let alone “insane”.