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The problem with Gen 4, is, there actually aren't a lot of good quality 'final team' options - referring to your chosen six that you bring to the Elite Four.
1. Remove all baby/NFE Pokemon, since you'll have evolved your pokemon by then.
2. Remove all Pokemon that are locked to post-Elite Four, like the legendaries, and all of the Pokemon that need special items like Gliscor
3. Remove the low-tier Pokemon like Kricketune, Wormadam, Chatot, etc.
4. Remove one of the fossil pokemon, and two of the starter pokemon, since you only choose one.
Remaining is a really small handful of 'solid' Pokemon. I found this pic Googling 'generic pokemon diamond team', uploaded with the caption "There is nothing wrong with the Gen IV 'cookie cutter' team and I'm tired of pretending there is" which sort of sums up how shallow the selection options are.
The games can still be fun, but, realistically, it limits replayability. Pokemon is like going into an ice cream shop. The more flavors available, the more 'happy customers' you are more likely to get, and the more you'll have people coming back to try different flavors.