Physical/special split wasn't necessary or good. It was implemented because EVs and natures required a "dump" stat with one of the attacking stats being the best option 95% of the time.
The all or nothing min-maxing of stats introduced in gen 3 wasn't healthy for the game, neither was movesets built of high power moves with perfect coverage off the pokemon's best attacking stat.
Specific examples of pokemon saved by the change:
>Dark types
Should've always been a physical type. Literally every dark type except houndoom has higher or equal atk and houndoom is also a fire type. Gen 4 only added darkrai to break the trend.
>Kingler
Ruined by crit mechanic changes, in gen 1 crabhammer had nearly 100% crit which covered for its low special. Water/normal was also unresisted
>Gyarados
Lost its special attack in the transition to gen 2
>Flareon
Lost special attack in the transition to gen 2, still a slow fire type
>other various mixed physical/special dual types
Were generally fine using their lower attacking stab as coverage

The list of pokemon "saved" by the split is quite small, sure many pokemon benefitted, but if everything benefits its just power creep.

P.S. we could've had no split and a few signature moves (like crabhammer) changed to be physical