Notice that the scrolling text that's missing from the 6100 does show up on the scope... which tells you that it's a problem with the Z circuit. The 6100 respects the Z and blanks those vectors, but the scope shows everything coming out of X and Y.
But if Z is broken why do you see anything? Because it's a problem with the Window circuit, whose job it is to blank only certain (programmer-defined) areas of the screen. it was used in Battlezone, for instance, to keep the battlefield out of the score and radar area at the top of the screen. Easier to do it by setting a window boundary than by trying to calculate and truncate each vector that might be going too far. It is used in MH for the credits crawl as well as the scrolling maze phase of the game... which is fascinating to watch on the scope. On the scope it's jerky and frenetic as extra segments are drawn past the top. With the Z controlled by the window circuitry, you get a nice stable boundary which really improves the perception of smooth scrolling.
The Window circuit is on sheet 8A of the schematics, so make sure all those components are correct and all pins are soldered. To troubleshoot you'll have to probe through it while attract is running and catch it while it's being used. When you have a signal on VYD11, make it makes it all the way into pin 16 of 12D (that's when the boundary is being set by the programmer). It is supposed to turn on the switch at 12D and connect the Y Window signal (from the Y Output stage) so it gets amplified by 12C and 9K and sent to the RGB Output circuit to create the ZBLANK signal coming out of 8K. That is used to clear (or not) the flip flop at 13J which is the final arbiter (before the buffer at 13K) for the Z levels for all three colors (sheet 9A).
As for CR8 going in backwards, and possibly contributing to malformed and/or shaky vectors, I'd replace Q7 and perhaps Q6, and try a new DAC-08. It's all in the circuit called Linear Scaling but keep in mind it used for all scaling factors including one (in other words, it's used all the time).
PS. Yes the speed of the 6502 can wreak havoc on the game if it cannot run fast enough. The 6502 will run at up to 1MHz, the 6502A up to 2MHz, and the 6502B up to 3MHz. You may get lucky with an CPU that can exceed its rated speed, but it's not guaranteed.