TCPi can kind of have both ways.
Let's say Shaymin EX is intended to be a staple for the entire season, TCPi can release the tin later in the season, after the 2nd or 3rd set of the year. By this time many of the serious competitive players will already have playsets, will have already bought boxes/crates trying to pull them, and will have already gotten plenty of use from them. This opens up Shaymin EX play for more casual people, parents, and people who play on a budget. These specific type of players don't look at, say, the Blastoise EX tin and think "hey, I could throw one of those into my build", but they would with Shaymin EX. Shaymin is also a popular Pokemon that will garner the interest of collectors, even those who own both version of the ROS Shaymin EX.
Let's say Shaymin EX is intended to be a staple for the entire season, TCPi can release the tin later in the season, after the 2nd or 3rd set of the year. By this time many of the serious competitive players will already have playsets, will have already bought boxes/crates trying to pull them, and will have already gotten plenty of use from them. This opens up Shaymin EX play for more casual people, parents, and people who play on a budget. These specific type of players don't look at, say, the Blastoise EX tin and think "hey, I could throw one of those into my build", but they would with Shaymin EX. Shaymin is also a popular Pokemon that will garner the interest of collectors, even those who own both version of the ROS Shaymin EX.