Not only do I think changing the type chart would be the Pokémon equivalent of opening up Pandora’s box, but I also think these changes are a bit too hypothetical for my liking. Yes, there’s still some disparity between the best and worst Types, but we’re in age where generational power creep has developed so much that Pokémon can be overpowered and/or broken even with poor offensive or defensive typing. Are there things that could be changed about the type chart? Probably, but it stands to reason that stronger game balance could be achieved by addressing the things that are actually breaking these Pokémon in the first place. The problem is, there’s no set definition for what makes a Pokémon truly overpowered or underpowered, especially not for the sake of a community like this with several unofficial competitive metagames that have wildly different rules than what you might see more often in the actual games.
Case in point- the Steel-Type is so good not only because of its many resistances, but also because of factors like a Toxic immunity, immunity to Samdstorm, and a Stealth Rock resistance. How often do those things show up in single player, though? Or in officially licensed VGC formats? Conversely, I personally think Grass is the worst single Type in the game (or at least tied for the spot with Normal and Bug), but that hasn’t stopped Grass-Types from tearing it up in modern metagames with consistent results, regardless of their less consistent single player results.
Interested to hear your reasoning for this, because I'm honestly not sure there is a worst type. There are certainly plenty of type combinations that are absolutely horrible and nigh-impossible to salvage (I'm thinking of Grass/Bug, Fire/Rock, and Grass/Dark as immediate examples - ironic that Grass plays a role in two of those) but I'm not sure there's a clear-cut worst type overall.
You can use outside factors like average BST to weigh them up - by which metric Dragon almost certainly wins hands down - but in terms of type advantages and disadvantages Grass is equally as vulnerable as Rock (both have five weaknesses) and offensively it's equally as poor as Bug (both are resisted by seven types). So an equal case could be made for Bug and Rock being the worst type, but then that's not even taking into account Ice's lack of resistances or Normal's lack of advantages. And ironically despite Normal having no advantages I think there's actually a pretty strong argument that Normal is one of the better types overall.