New Subdomain & Best Way To Index

[Markbwc]

We have an ecommerce site, we'll say at https://example.com.

We have created a series of brand new landing pages, mainly for PPC and Social at https://sub.example.com, but would also like for these to get indexed. These are built on Unbounce so there is an easy option to simply uncheck the box that says "block page from search engines", however I am trying to speed up this process but also do this the best/correct way.

I've read a lot about how we should build landing pages as a sub-directory, but one of the main issues we are dealing with is long page load time on https://example.com, so I wanted a kind of fresh start.

I was thinking a potential solution to index these quickly/correctly was to make a redirect such as https://example.com/forward-1 -> https:sub.example.com/forward-1 then submit https://example.com/forward-1 to Search Console but I am not sure if that will even work. Another possible solution was to put some of the subdomain links accessed on the root domain say right on the pages or in the navigation.

Also, will I definitely be hurt by 'starting over' with a new website? Even though my MozBar on my subdomain https://sub.example.com has the same domain authority (DA) as the root domain https://example.com?

Recommendations and steps to be taken are welcome!