First, welcome back to the amazing adventure of writing on the World-Wide-Web if you took a break. I will try to address the questions in order & succinctly. I will answer based on my limited knowledge today while mentioning there is science to the marketing of Hubs. There is an overall strategy and two smaller - Search Engine traffic & Social Media. A recommendation is a Hub I wrote at my Profile about marketing Hubs as products with many resources to familiarize one to those two sciences.
The main question is yes because there is more. The more articles there are the more available standalone articles to market as products.
The 2nd is forget about Sub-Domains. Sub-domains were never ranked by Google independently. They were introduced to help the Website HubPages become ranked higher. Again, the power of ranking is contingent on the standalone article with its ranking. So, understanding Search Engine Optimization (SEO) principals and techniques is the key. Important is a premise is Content is King and Google incorporates that with their algorithms for ranking. So, does HP with the Quality Assessment Process (QAP). Help is at the following links for how articles are scored / rated at HP. The aim of the rating is being compliant with Google’s goals for articles.
Informational Articles: https://hubpages.com/help/hub_hop_table#informatio...
Creative Articles: https://hubpages.com/help/hub_hop_table#informatio...
3rd – when you had a subdomain you were always considered a HubPages article at the website. Your subdomain was never a website. Adding new articles always had value to the website – Hubpages and not the subdomain. So, yes HubPages is always having new articles added to it. However, HubPages today has a new strategy having aim with independent Niche Sites or Topical Domains. An article is chosen by HP to be transferred there. Go to this link for a little understanding: https://hubpages.com/help/sites-editorial-policy
4th – the loss of sub-domains did not affect my traffic at all. However, it did affect those with very high views generated by Google. Some worse and some better. So, kinda is a moot discussion especially with the new strategy mentioned above.
5th – Yes, naturally adding articles do increase overall traffic initially mainly because of the social network here at HP and sharing at social media sites like Facebook, Twitter, and Pinterest. Then its Ranking at Google takes over.
Humorously insert typical disclaimer here :-)