Unpopular opinion: BDSP is the best Sinnoh game. Also contrary to what people here say, BDSP has a lot of Platinum's content (something that people here intentionally omit), stuff like the expanded Platinum Dex, the Giratina boss fight, Gym Leader rematches and E4 Rematches, etc.
But more importantly (and here's the unpopular opinion), I think the decision to follow DP's blueprint over Platinum was the right decision.
Platinum made some weird changes to the overworld, like making the Battle Zone more tropical. Platinum also made Gardenia's gym worse (for my taste at least). And also, Platinum introduced Looker and Charon, both of which are stupid characters that don't add anything to the plot, and even make the plot worse.
As for the Battle Frontier, people overrate that feature a lot. The Platinum Battle Frontier is literally just the Battle Tower, and 4 more Battle Towers with slightly different rules. The BDSP Battle Tower is much better and more challenging in every way.
BDSP basically took everything good from Platinum, and kept what was better about DP.