The reasons its important, its because alabasta and ennies lobby have the most iconic matchups sequences.
And in these sequences, zoro fought the strongest goon, while sanji fought the next strongest.
Since Oda does indeed mix his formula a bit every arc, it didnt happen for a while. Why? Because there were tons of solo luffy arcs in The Middle.
Who did zoro and sanji fought and won in sabaody? Sentoumaru? No. Kizaru? No. They come back2 years later and they are the ones that find luffy and beat a pacifista together. They are the ones that can use haki, aside from luffy.
Zoro and sanji block the goons for luffy on FI, zoro takes oj the sword octopussy, who was the strongest goon, second to him, it was the giant dude, knocked out by sanji, something jinbei failed to do.
After that, they start fighting all over the place and then get separated in dressrosa. Only now in wano they come back together. And still they are put together side by side. At yasuie execution. They are the only 2 SH to clash with SN. But OMG if someone put them back together. What are they thinking? What kind of delusional bastard would put them together just because oda keeps doint it on a regular basis?