I generally agree with the people suggesting that the raiders should begin scaling up once the number-of-systems threshold is crossed, rather than from game start.
The main reason for this is user experience - basically, the setting is not behaving in the way that players are expecting it to, so there is a strong argument that it should be changed to function as players expect it to. I would note, for any other spoilers it works in this way, albeit accidentally (Swarm and Invaders do not 'develop' or grow prior to being discovered as they generate on discovery, and Precursors remain completely static AFAIK), so perhaps some of the confusion is that Raiders behave very differently from other spoilers with respect to the similar game setting.
Right now, the way to get this "expected" behavior is to turn the Raiders off at game start and turn them on in the game settings at a desired point in time. This is a bit unintuitive, and I thought was the reason why the number-of-systems trigger was added was to avoid having to do this, e.g. for Invaders to prevent discovering an Aether Rift one jump from Sol and dying in five years.
The one thing I think is left uncertain is how to preserve the current behavior, i.e., the Raiders grow from game start but will not appear until the player has expanded a bit. However, I think it is an open question if this behavior is the one many players want to use, I think most players want the "expected" behavior described above (for slow/conventional starts) or they want 100% risk from the start of the game (for traditional/high-pop TN starts), not so many seem to want the in-between?
Changing the game settings might also be a good idea. He could start with 4× population, like Steve did in his most recent AAR. That would give him more forces at the start of the game, and more exploration ships to survey those first 10 systems more quickly. I don’t know if he had any NPRs enabled at game start, that might have helped as punchkid surmises. He could have set the raiders to attack after the 5th system is explored instead of the 10th; they would have had half the forces and he would have had half as many colonies to protect.
I really do think, on a side note, that the default population for game setup should be 1b. When I started playing I quickly found 500m to be very slow and limiting, and with the new spoilers I think this is even more of the case. Of course the player can and usually will set it to whatever they want, but I think it is good to have a more reasonable default to set the expectation for new players.
