The new search suggestion feature which uses WVUI enforces a font-size for the suggestions that is too big. I did not have the time to look for the actual source code, however, from what the browse console tells me, this is the relevant CSS portion:

.wvui-typeahead-suggestion__title {
    color: #202122;
    display: block;
    margin: 0 0 2px 0;
    font-size: 1.14285714em;
    font-weight: 700;
}

If font-size: 1.14285714em; is not used or font-size is explicitly set to 1, things look much better, and much more similar to the search results form legacy Vector.