That is because you did not have 2 levels of multi-tenancy. first you have schemas inside one database. Next you can have multiple databases where these schemas live. If you want a single tenant to a database. Simply make a database with one schema for those resource hungry tenants.
Tooling is key here. Java spring, for example, can do that. Not that easy though and requires a lot of knowhow for a lot of edge cases.
The main problem with multi-tenancy like that is migrations. It can take a lot of time. There are 2 strategies: backward and forward compatibilities. Or, green blue deployments with ISITIO or equivalent tooling (e.g. if one server is behind it is still routed to the old front-end).
The main problem with multi-tenancy like that is migrations. It can take a lot of time. There are 2 strategies: backward and forward compatibilities. Or, green blue deployments with ISITIO or equivalent tooling (e.g. if one server is behind it is still routed to the old front-end).