In this FFF you asked the question of "How did we not notice it for like 2 years?" regarding the biters being bugged regarding belts. Well, although I believe the question is 99% rhetorical I DO have a very specific and personal answer to it:
Because you (wube) dismissed my exploit report from back in 2017-02.
I mentioned it in a reply to "FFF#177 - Difficulty Settings". Right after I brought the biter on belts mechanic to your attention as exploitable to the point of rendering biters incapable of attacking, it (and other considerations) were dismissed as "None of this is anything we care about trying to prevent." by Rseding91. (I am not mad at you Rseding91
)viewtopic.php?f=38&t=41110&start=80#p242953
(The picture was deleted by the filehoster by now. It showed a line of turrets and in front of them a ~4 to 5 tiles deep blue belt carpet.)
Back then I perceived the implementation of the enemy threat as a huge neglect by wube (I still do, but the Rampant mod and Redmew scenario servers do a fine job of enabeling me to live with it). Not particularily because of this exploit, I just had high demands on the challenge posed by the enemy threat and the environment. Although Rseding91's reply baffled me (wube spends time and resources to implement the attack and movement abilities of the biters but at the same time allow some simple exploit to render them useless), I believed him, because it was pretty much in line with my perception of how unimportant the enemy behavior to pose a challenge is to you. After a final, general lammentation to Rseding91 I quit. Thus this exploit never made it into a bug report or a general discussion on the forum on my behalf.
In other regards than the biters, Factorio went a long way since back then. Great job guys! Posts suggest back in 2017-02 there wasn't even a sharable blueprint library. Imagine that! ^^ No one would want to go back there.
Imagine january 2020. A time after the final release. Imagine reading: "In march 2019 factorio was not yet equipped with the final, smarter biter war logic. Players had to install mods so the biters would even try to find weak spots in a bases defense system. Imagine that! And the other things they added to make it smarter and more fun? ... The simple biters from before would be outright boring in comparisson today. No one would want to go back there. And look at all the reviews, mentioning the smart and challenging biter logic!"
Well, I guess, my attempt to - again - make you think about making the biters a bit more strategic and smarter, is pretty blatant.
