求填空中presumably的用法

kate_25UID：3509305

Magoosh中的一题
Some note that the increase in the Native American powwow--an intertribal
affair of song, dance, and storytelling, all intrinsic aspects of Native American
culture--serves to (i) ______________ the very culture it presumably aims
to (ii) ______________. They argue an overarching cultural narrative
emerges, one that (iii)______________ the narrative of any one tribe.
Blank (i)erodedistillempower
Blank (ii)fosterunderminequestion
Blank (iii)subsumeselaborates uponovercomes
答案是erode，foster，subsume

解析中说第二空跟第一空根据presumably可知应该是个相反的概念。
可是presumably的意思不是大概，可推测吗？为什么有相反的作用呢？

crazyrobinUID：2368627

presumably |priˈzo͞oməblē|
adverb [ sentence adverb ]
used to convey that what is asserted is very likely though not known for certain: the Yakima Indians presumably came from Asia by way of the Bering Strait.

小海洋UID：3530868

Some note that the increase in the Native American powwow--an intertribal
affair of song, dance, and storytelling, all intrinsic aspects of Native American
culture--serves to (i) ______________ the very culture it presumably aims
to (ii) ______________. They argue an overarching cultural narrative
emerges, one that (iii)______________ the narrative of any one tribe.

一些人发现传统美洲人powwow活动的增长（powwow，部落之间关于所有本质文化的歌曲、舞蹈、讲故事的活动），反而损害了本来应该致力于将文化变得更加繁荣茂盛的目的。他们提出一种包罗万象的文化现象的萌芽，这种文化现象能包含任何部落的文化表现。

yifeir1UID：3534487

我理解的presumbly在这的意思是：原本，本意的意思