Not at all? If I was porting a game, I'd at least want to make important behaviors 100% true to the original - accelerations, jumping physics, hitboxes, speeds... these are pretty tedious to reverse-engineer without source. OTOH, the source was assembly and the binaries could be disassembled...
I think you underestimate how different the original game and port targets were, and overestimate how capable the machines the porters had access to as workstations were.
And that ZX Spectrum port is brought up all the time when people talk about great Spectrum games, while it is, at best, kind of themed the same way as the arcade original.
The result was in practice a lot of this would be done by playing the arcade machines and then attempting to replicate the feel on the target (which is why so many ports miss easter eggs), and at that the C64 did remarkably well here.
The Atari 2600 Pacman is the canonical example of this going wrong.
There's a bit about the port as a section of a longer discussion about publisher Firebird: https://youtu.be/LWHJomIX_As?feature=shared&t=2297 . Which does state that yep, it was mostly made by playing the arcade game lots then doing the best they could. They apparently did have some documentation... in Japanese.
AFAIK "here's an arcade PCB, write this for the C64 / Speccy" wasn't an uncommon thing back then. Arcade perfect wasn't really a thing for the 8 bit micros...
> If I was porting a game, I'd at least want to make important behaviors 100% true to the original - accelerations, jumping physics, hitboxes, speeds... these are pretty tedious to reverse-engineer without source.
You're wildly overestimating how professionally done a lot of video game ports were in that era. It wasn't uncommon for home computer ports to be written by a single developer whose only access to the original was being able to pump a pocketful of quarters into it at their local arcade.
Frame rates varies widely, resolutions varied widely. The exact behavior was in e.g. pixels/frame, and you had to work hard to get the same feel on a 50hz 256x192 4Mhz z80 ZX Spectrum, as you did on the 60hz 160x200 1Mhz 6510 C64 ; Also abilities differed widely : C64 had hardware sprites, tile (text) mode and hardware scrolling; Spectrum had nothing but a frame buffer (it did have a much faster memory copy instruction, LDIR, but that didn’t compete with hardware scrolling).
And the original arcade, of course, had multiple playfield with hardware scaling, and often game-specific hardware (in the early days at least)
