Examples: Virtua Racing on the Genesis or Star Fox on the SNES. they were slow and quite laggy. sure they were essentially pushing the limits of what the console could do and in the case of Star Fox had to have the FX chip in the cartridge but I wouldn't call racing around on the Genesis in Virtua Racing a "smooth" experience.
Other games are like this too with loading. Mortal Kombat CD on the Sega CD. you get to the Shang Tsung fight and the game has to load every time he morphs. Other games would also slow to a crawl if there was a lot on the screen. To your point Ranger X on the Genesis had these little tadpole enemy things that could quickly populate the screen if you didn't take them out quickly it would slow the game down. Same would happen on the PSX with the game Loaded.