Despite Google saying that they treat subdirectories and subdomains the same that is not the case. So many examples of sites that create subdomains that see drops in traffic and visibility and when they bring it back to the main domain as a subdirectory they get the traffic back.
I know that subdomains are much easier to create which is why most sites will do that – but the LOE to mask the URL via reverse proxy is well worth the payoff.
Why, because subdomains are treated as a separate and brand-new site even though it’s part of the domain.