I, uh. Think the older folks that are going to strongly associate DK and Mario are... more like 40+, not 30+? Being in the mid thirties and growing up with that stuff, the strong connection is earlier than that, with the original Donkey Kong. After that it was over a decade before the two series came together again meaningfully with SSB, and most of it beyond SSB is relatively recent.
Most normies in that age range wouldn't really think to connect the two, outside maybe both being major nintendo franchises. The older stuff didn't have much connection past the original arcade game.
This. I know it started with the DK arcade game but they've been separate properties for 3 decades at this point. It's Mario and Yoshi, not DK.