McCoy primarily played guard at aTm.
The 2019 Saints signed Nick Easton after Max Unger retired, with plans to play him at C. It’s possible they were planning to shop Armstead, who had missed six games and didn’t finish two others in both 2017 and 2018, and move Peat to LT as his rookie contract drew to a close. That would have been McCoy’s opening at LG, leaving an OL of Peat-McCoy-Easton-Warford-Ramczyk.
With Armstead remaining in the mix then playing 15/16 games, Peat never moved outside. Easton didn’t win the job, but then Warford was let go. Drafting Ruiz in 2020 to move McCoy to LG would have given Peat-Armstead-Ruiz-McCoy-Ramczyk as the plan, but Covid-19 messed that up so they rolled with McCoy at C and slotted Ruiz at RG.
If this all checks out, it looks like their plan was mainly marred by circumstance.