What you say is not true.
If we look at preTS, in terms of lethality, shishisonson is probably number 1 despite being 1 sword style. If more swords = more lethality like you are implying, he would not use 1 sword style to cut something that he failed to cut using 3 sword style.
More swords for Zoro means stronger/ more powerful attacks. This is self evident when you have 36 pound canoon with 1 style < 72 pound canoon with 2 style < 108 pound canoon with 3 sword style.
If we look at preTS, in terms of lethality, shishisonson is probably number 1 despite being 1 sword style. If more swords = more lethality like you are implying, he would not use 1 sword style to cut something that he failed to cut using 3 sword style.
More swords for Zoro means stronger/ more powerful attacks. This is self evident when you have 36 pound canoon with 1 style < 72 pound canoon with 2 style < 108 pound canoon with 3 sword style.