It's fine to argue that you don't need more than 5GB - I don't know you and would certainly not, unless asked, attempt to judge how much email you need,
However, your needs, let alone your desires, are unlikely to be the same as others. They may not even be the same as the majority of others, let alone most other people.
People have very different patterns of professional and social interactions. For example, the email storage needs of someone with a tiny circle of friends is likely quite different than someone who has many friends and is active in many organizations and is perhaps a "goto" person in some of those. As well email "needs" are not determined solely by the number of contacts but also the nature of communications with those contacts.
Of course I don't "need" the more than 15GB I currently have in my email folders - in fact, I don't need a computer, internet, a phone, or even electricity. However I choose to have all of those things.
Someone with severe OCD may keep their home spotless and perfectly staged so it's always ready for a photo shoot by Architectural Digest with five minutes notice (perhaps even putting their plants on hidden rollers so they can move easily as as plants and furniture apparently do spontaneously during such photo shoots!). Others choose to allow a bit of clutter and use the time, energy, and money saved on other things. Email is not much different.
Of course Google is free to set whatever quotas they want and charge whatever they want for storage - and I don't need Google services at all (I choose to use some of them but also choose to buy similar services from other providers even though Google might provide them for "free" today).