That's a bit odd, probably about 95% of my 1v1 matches are lag-free. You can speed up your connection by...
- Going closer to your modem/router, in the same room as it
- Not doing anything else on the internet while you play (especially watching videos or streams)
Doing those can actually speed up your connection quite a bit. I hope your lag stutter problem goes away. Keep in mind that there will be matches where there is lag regardless of how good your connection is because a lot of people that play online Smash don't have fast enough internet and/or go against the above tips.
I know how crucial it is to have lag-free matches in frame-reactive high-speed fighting games...