In order to illustrate what Sik said here, I decided to run the Genesis port of Joe & Mac on Exodus emulator and take some notes:
In a recent interview to Sega-16, the developer of this port said:
Full interview here: http://www.sega-16.com/2016/05/inter...art-middleton/The Genesis didn’t have enough memory to contain the levels, so we came up with a process where we could copy across new background graphics on the fly so that we could get everything in. The sprites were more of a challenge, but Tim worked really hard to faithfully reproduce the game with the limitations of the Genesis compared to the original arcade machine. We did have to cut back in some areas, but I think they were few and far between.
When you're running this game on the emulator you can notice that it updates/replaces part of the VRAM with new background tiles every time the screen scrolls a little bit; so it works exactly like the developer described in the interview.
By doing that, he managed to free up some extra space for the sprites, which I calculated (measuring the size of the address range of the VRAM areas which contain sprites) at around 22 Kbytes (or more; I believe it uses up to 24 Kbytes in some moments) in any given moment when you're in 2P mode.
So I think that's a good example of what Sik had stated and a situation where it clearly surpasses the sprite memory limit of the SNES (16 Kbytes).
Also, by observing the sprite list you can see how the flexibility of the Genesis sprite table is useful for games like this. Several different sprite sizes were used there, while on the SNES you'd be limited to only two of them and it wouldn't offer the non-square ones (like 8x16).
And all those limitations were pushed with only 60 sprites on the sprite list (usually not all of those sprites will be shown on screen at once at any given frame) (80 sprites would be the maximum for that resolution on the Genesis); that's why knowledgeable people such as Chilly Willy always called "bullshit" those specs vs specs comparisons where the SNES is sold as the console with the superior sprite system by just mentioning that its maximum number of sprites is 128 (against 80 on the Genesis).
PS: Just as an additional note, the VDP registers window tells that the game often uses DMA transfers of length 1 Kbyte in order to update the VRAM.