Having the ability to import from IronVest would make Proton Pass much more appealing to change to, otherwise it would be a lot of work to re-create the accounts and passwords I already have.

Never used Ironvest, but most password managers allow you to export passwords as a CSV file. It is a plaintext file, but it works. The reason why Proton likely have a hard time with all the importing of passwords is that there are very many places people store passwords. Such as Bitwarden, Google, 1password and many others.