Very simple: release the DLL source code.
Yet, when they'll do it, I'm not going to work on the AI, as there are a lot of other things that take priority for my enjoyment of a Civilization game, like diplomacy, combat mechanisms, more units per tile, etc... No point in starting by the AI when all those changes will affect it.
This is worth mentioning in its own right actually. AI and the design of the game are not completely independent, just like the design of the game is not completely independent from the player. In making templates onto which DLC will be added later, games do lose out on some ability to make decent AI by necessity.
It's another side of the coin in terms of Civ 6 problems - a lot of its mechanics actually don't make sense if everyone in the game is trying to win...which means either those mechanics or the victory conditions are misaligned. Making the AI (or human player choosing) to do one comes at the expense of the other. This isn't the only reason the AI is bad, but it doesn't help and it puts an unnecessary upper boundary on AI quality by design...
I think bad journalism is THE problem of our society in 2019 and game reviews show that really good.
They're just the tip of the iceberg. Were they the only problem with mass media the world would be much better, but sadly no. Still, it's worth pointing out when "professional" publications lie, regardless of context. Firms that do that are in essence scammers, promising a service that goes unprovided.
So you want to have a bad AI for years until every feature is in the game and only THEN care about the AI?
Rather, since the AI acts in the role of a player each new feature must be aligned with the AI capabilities (and vice versa) for games that do single player.
Firaxis straight up doesn't care. It has implemented numerous things into Civ 6 that basically don't work in competitive MP. That is all but an open admission the AI isn't a serious priority, but it also means they don't mind obvious holes in terms of their design having obviously broken incentive structures/choices. I'd be inclined to agree that the AI can't easily be made good without fixing the game's design itself first, because doing so would mean instructing the AI to blatantly ignore quite a few mechanics in the game while trying to win...
Small, focused improvements could be released pretty quick I suppose (ie days/weeks), and you could have a globally "better" AI a few months later, but for a "good" AI (OK, that's subjective) I don't think that "years" is an exaggeration.
That's the course AI mods in Civ 4 followed. You saw some improvements quickly, but over year(s) it kept improving and eventually became substantially better than vanilla/BTS variants. Much of this happened post-BTS, however, where the game barely changed after that.