Subs are critical. Growth is critical. The higher the rate of sub growth, the more Yt will notice your channel. On the corporate side, sponsors, MCNs, and Youtube, throw resources at you the higher your rate of sub growth. Think of it as horses in a race; everyone wants to back the strongest horses on the track. Algorithmically, the more subs you have, the better your video does out the gate - there are more eyes on it in a short amount of time, giving it high view acceleration and high virality. A high sub channel (say 1M+ subs) can have a Seo naked video, and get 500k views in a few hours, bypassing a 1k sub channel with fully Seo'd videos, in the blink of an eye.