In the account portal, use the initial of the account's first name instead of last name and show the name in the format "First Last"--except when there is a nickname, in which case use the nickname. The circled letters seem designed to differentiate between linked accounts, so I can foresee families in which everyone is labelled with the same letter and you can mostly only see the last name.

(This would only apply when there are multiple accounts. I agree with this idea when there are no linked accounts: https://ideas.iii.com/forums/951766-vega-discover/suggestions/50968153-suppress-the-patron-name-when-account-linking-is-n)

Also, use the first name, or nickname if there is one, in the Overview where it says "Welcome 👋 [name]!"