Deck question- plywood needed for screws?

[ElBichoMalo]

Working on my deck now. I am using 3/8" divinycell, but was planning to use fir plywood in the "fastener" areas, like for the console and leaning post. Basically same as factory, where plywood instead of balsa. Now I am thinking I don't need to do that at all.... If I plan to over drill and fill with cabosil for all of my screws anyways, then why not use all divinycell?

Can you confirm my logic?