Having purchase and played both SMB3 and SMW when they came out, it’s beyond question that SMB3 is superior.
SMB3 came out later in the NES life cycle. It has both horizontal and vertical scrolling, which was somewhat unusual (though not terribly rare). The music was great, the graphics were great, the gameplay was great, there were a huge number of levels, tons of powerups, etc. All this was new to the Mario series at the time.
By contrast, SMW feels like a release title. The graphics are lackluster. Even at the time, I felt that the backgrounds and textures lacked “depth” and were boring, bland colors. (Like, compare the graphics of SMW to like, Star Ocean or Tales of Phantasia). The gameplay didn’t improve on SMB3 whatsoever, and is actually worse in many regards. The cape was a shit replacement for the racoon suit. Sure, SMW added Yoshi, but that’s all it brought to the table. I’d even argue that Yoshi wasn’t a good gameplay mechanic because it allowed Mario to get hit and just jump back on Yoshi — sort of like how Sonic can stay alive if he has just 1 ring, which you can collect each time you’re hit. It threw off the balance and made the game laughable. Plus the world themes weren’t as compelling as SMB3. There’s no iconic “big / small world.” Instead we get a cave world, a haunted woods, etc. Wooooow. The epitome of a “release title!”
If by improved you mean made worse in just about every other way with maybe the exception of sprite flicker and additional actions facilitated by controllers with more buttons, then I agree.
Games progressively became full of badly written long-winded dialogue; tutorializing; patronizing design; handholding; and all set to worse music, and usually with worse aesthetics. Every era has at least a spattering of good-to-great games of that type, but the NES era is the pinnacle of beautiful intense scrolling action games.
You just have bad taste, use emulators/digital displays, have poor dexterity, or most likely all of the above.