The philosophy behind introducing new maps is good and I have no problems playing this map in the season (despite the fact I think it looks like a clustered back-cap central).
The problem is that the philosophy is stupid when the team is removing other new maps. Sunshine was for the most part quite well received, and is a common map I see people scrimming/pugging often. It's definitely faired far better than Reckoner in that regard anyhow. If you want long term variance in the map pool, then it would have been in your best interests to keep Sunshine in the pool and instead replace a different map.
Imo Prolands or Granary were ideal candidates to be substituted for Cardinal for this one season, considering that Collaide confirmed that there is no intention for Prolands to be developed further, and you're not going with the newer version of Granary for reasons unknown. Based on Stinson's reasoning, it simply doesn't make sense that you'd remove Sunshine over these two perfectly more valid options.
Alternatively you could just stop making these out of nowhere decisions without consulting your community as Eemes said, but that's probably a preach to the choir based on history.