First I want tell something, if you don't want to see a full-scale battle between Luffy and Big Mom please don't read this blog. I personally hoping for a big clash as Totto Land finale. Like we saw in Dressrosa.
Allow me to explain why I hope/think the battle with Big Mom and her crew is necessary and unavoidable.
Luffy and his group turned upside down the Seducing Woods and some part of Whole Cake Chateau. Cracker defeated by Luffy (and Nami) and severely injured in the process. Chopper and Carrot invaded the Mirror-World and took Brulée as hostage. Jinbe burnt Mont-d'Or's collection of books when he saved Luffy and Nami. Nami and the others rescued Brook from Big Mom's clutches totally fooling her and her three strongest homie in the process.
Even if Big Mom could overlook these, she can't be sure Brook doesn't copied the poneglyphs. And if Sanji rejoin with his friends and try to leave Big Mom will lose the chances to finish her plans to the wedding. So I think these enough troubles for Big Mom to take the matters her own hands and chase them personally.
Luffy has two objective in Totto Land: Sanji and the poneglyph. The last chapter suggested Sanji will rejoin Luffy's group and Brook's success with the poneglyph mission, they obtain both target and want to sneak out Totto Land. And I think they will continue how the pirate alliance planned back in Zou. They will head towards Wano.
And this is the point where the big clash with Big Mom and her crew is necessary. (In my opinion.) If Luffy don't deal with Big Mom in Totto Land and try to escape to Wano, the Straw Hats will be in trouble. In Wano, the Straw Hats want to dethrone Kaido, one of the Yonko. And Kaido is a terrific and powerful foe. Luffy and his alliance can't battle against a powerful foe in front of them if a likewise powerful foe is in there back.
This is why I think and want/hope for a big clash in the end of Totto Land.
P.S. If some of you guys are admins and you see something I wrongly edited (title or else) please feel free to correct it. Of course these are just my personal opinions and hopes so don't be angry with me and please comment it if you feel that way.