Migrating our on-premises team site collection and its sub-sites, to follow the flat structure..

Hi All,

I am facing this problem, where i need some advice on it. Now we have an on-premises site collection which contain 2 levels of sub-sites, and i want to migrate the site collection an its sub-sites to SharePoint online, but i want to have the migrated sites created based on the flat structure.

Currently we have the following inside our SharePoint on-premises 2013:-

1. We have a site collection based on the Team site template. Named “Projects Home”
2. Under the site collection’s root site, we have a sub site named “Projects”.
3. And under the “Projects” sub-site which have around 20++ sub-sites of type Team sites (sub-site for each project).

Now I want to migrate the site collection and its sub-sites to be inside our office 365 tenant. But I want to have the following structure (which will be compatible with the modern flat structure):-

1. To have a hub site collection representing the “Projects Home”. This will be a modern communication site.
2. To have another hub site collection representing the “Projects” sub-site. This will be a modern communication site.
3. For all the 20 sub-sites to have them as 20 modern team site collections (which have office 365 groups), those will be linked to the “Projects” hub-site, and the link can be done manually later on.

now i have third party tool named sharegate which can do the actual migration. but i am asking a question, if i should have my on-premises sites created as site collections and hub sites? or it is better if i migrate the on-premises site collection, to be a classic team site that have sub-sites  ?

now i am sure if i want my on-premises sub-sites to be migrated as modern team site collections, then this means more work and more complexity. but i am trying to follow a future-proof appraoch, as seems having sub-sites inside sharepoint online, is becoming less advised and are being considered as old appraoch compared to the flat structure?

 so would like to get any adivce on this?

Thanks