Almost certainly it's the fact that you're talking about multiplayer while he's talking about single player.
In single player it is certainly a possibility to build "too many" units, in that their marginal utility declines after you have a certain number to the point where it isn't worth the gold they cost to maintain.
In multiplayer tactics are more important than in SP so Keshiks rule. In single player ranged units do the bulk of your fighting to achieve high kill ratio against the AI and so Keshiks rule.
Keshiks are like easy mode.
Keshieks are even stronger in SP turn based combat because there is zero opportunity to attack them. In MP you can at least get a quick hit in before they run away. A handful of Keheik can single handedly take over the entire world in SP because they never get retaliated against.
More production is always better. To say a civ is bad because it has too much production is like saying that Bill Gates is a loser because he has too much money. This is absurd. If you have nothing to build and no reason to make units then build workers and delete them for gold.
Then when something useful comes up like a wonder you build it in 4 turns flat.