Update: I did some testing in game
It seems that java kb (at least in 1.9) is used on cc bedrock. 3.5 blocks (or so) for first sprint hit, 1.5 (or so) for subsequent sprint hits, assuming your opponent doesn't move. One of the problems with kb that we are seeing is with delayed kb. With reach being about 2.5 blocks, the kb delay is enough that if you hit your opponent while they are running at you, you will run through them within a couple of hits, even when w tapping. The delay also allows your opponent to hit you back before they get out of range, completely ruining your chance at getting consecutive hits on them, and thus preventing combos. Another problem is hit delay. It seems that the time between hits is higher on cc bedrock than in vanilla, which means you are unable to hit people until they have taken most of the kb the previous hit dealt, which is not ideal for combos since it allows your opponent to hit you back more easily.
I am not an authority on pvp, but I will try to give some advice and quote some people who are. It seems that s tapping, which has the same premise as w tapping except you tend to not move forward as fast, may work as an effective way to combo people or at least keep them in front of you in combat. Perhaps a more exaggerated s tap could help combat the long hit delay that cc seems to have.
View attachment 176895
View attachment 176896 (sw leaderboard players)
Another tip is to strafe. This may not only cause your opponent to miss their hits, but reduces your velocity in the direction you're hitting people in, allowing you to keep them in front of yourself despite delayed kb. Although I personally do not utilize w or s tapping, strafing has allowed me to get several consecutive hits on opponents - even on skilled players.
View attachment 176897 (#1 sw solo player on how to get good at pvp)
It also seems like vertical kb on cc is less than what it is on java (and maybe even vanilla bedrock) as well. Since reach extends from players' eyes, less vertical kb makes the effective distance they get knocked back shorter. This, coupled with the aforementioned hit delay, is another factor to why comboing is difficult on cc bedrock.
My explanation may not be accurate at all tho, but I think the tips I gave are at least somewhat valid.