Why do you think WOTC nerfed them so heavily in 4 and 5e?
Because they adopted the cancerous philosophy of balance.
We have a topic about people arguing about whether there should or shouldn't be voiced protags, unlimited ammo, etc etc. It's pretty obvious that if you don't want to be OP you shouldn't pick an OP class. These discussion always end up coming to the compromise that we must give the other side the option to satisfy their needs. What you suggest would take the option of being OP or UP from players who want that experience, in the name of some nebulous "balance".
show me how a weaker class in 3.5e can dominate in the end when stacked up against a stronger class
A literally meaningless question in a single player RPG. You assume there is supposed to be some equality between a hard working wizard and a lazy rogue who always takes the easier path. It's a flawed assumption.
If they want to be OP, make them mod for OP-ness
If they want balance, make them mod for balance.
Keep in mind I'm also in favor of peopel being able to play the underdog classes.
balance in D&D should carry over here
Balance should be purged by and large. Classes should have their own independent identity regardless of how they perform compared to each other. A rogue is a rogue regardless of how well it performs vs a wizard. We must do away with the arbitrary limit that classes should only be allowed to exist if they can compete with another class.
Based on the rules of a multiplayer game
Literally does not matter because the product is going to be single player with the option of co-operative multiplayer. Everyone can decide for themselves what they want to be. FURHTERMORE multiclassing exists for those people who feel they picked a wrong class and don't want to start over.
most singleplayer games try to achieve a balance between selectable characters
Hence the decline of the gaming industry in the last decade.
never have seen in practice
Maybe you should play more videogames?