SDS has clearly stated in the past they work on a 3 years cycle, I don't know why people expect huge changes for their modes during the years outside that. They went Franchise --> Diamond Dynasty --> this being year 3 of the cycle of RTTS. And if you look at the difference of RTTS from what this one will have to MLB 16 it's night and day. They are obviously going to update DD as their money maker along the way, but the investment in DD from 14-16 was huge (the 3 year cycle). I guarantee next year for MLB 20 you see the Franchise cycle start again.
It makes sense in a manpower sense, they can't make major changes every year to every mode. It takes a few years to really refine it, so they'll tweak as they go. Franchise is on deck.
And if there is one company that can be be trusted, I truly believe it's SDS. You can already see the shift as they move DD rewards to other game modes and especially Franchise mode with March to October, the shift is on. And in their stream of it they said you have the option if you fail or win at it to just continue on in Franchise with that team - they're moving the needle.
They are the pinnacle of sports games. Think about it, they've released over 5 hours of previews to their modes, just to scratch the surface of what you can do, and still not done, the big announcements are coming this week. A game like NHL hasn't changed in 5 years, and they will release a 30 second "gameplay trailer" on outdoor rinks for an entire year of effort. This is EA and 2K vs. small studio SDS. This team takes their game seriously. The others, want your micro transactions. They prove that there is no excuse for the other sport franchises to deliver the trash they do.