I don't think anyone is saying they know how much time and resources it took to implement retro mode. But the development team has been very open about not being able to implement everything they want to every year and that decisions have to be made.
For example, in last year's stream they talked about how they did not expand on replay reviews. Someone explained that the boss came in and said, we can either do all these cool things we've wanted to do, or we can work on replays at 2nd, 3rd, home etc. The team chose to do all those other things.
Because of conversations like that, I think fans have adopted that mindset. Many also feel this is one of the smaller AAA development teams out there, furthering resource constraints.
That being said, I don't think retro mode took a lot of time and resources to implement. It seems like tweaking the gameplay and presentation to look more arcadey.



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