The OP mentioned they were struggling not so much with document exchange as getting a new word processor (Pages) to do what they want - in this case, easily navigate a long document. Pages is not functionally able to replace Word 2011 in this regard; in fact, there are lots of areas where the bloat/feature-rich Word trumps the simple/feature-stripped Pages.
I also find Word/Office to be bloated and despise the 'Ribbon' UI. But the reality is that its biggest weakness is also its greatest strength - among the features you will never use, you can be certain the one you actually need from time-to-time is there. For me, that includes the ability to display facing/multiple pages and, like the OP, navigate large documents easily via both a header-based navigation pane or page numbers.
Pages, while beautiful in its simplicity, lacks these pretty basic functions and I don't see the point of iWork '09 as it's almost a decade old with no update path. High Sierra is already breaking UI/functionality so it doesn't have much life left in it, sadly:
https://forums.macrumors.com/threads/iwork-09-crippled-by-high-sierra.2076344/
One last thing on Word 2016. The desktop version is actually pretty slick and feels much more Mac-like these days. But I'm staggered by how utterly crippled the iOS version is. Considering you need to pay for an Office 365 subscription to use it on an iPad Pro (both 10.5 and 12.9, due to MS's screen size licensing policy), it's a huge disappointment - the aforementioned navigation tools are a glaring omission (that even Google Docs has!!!). Bizarrely, Word Online in a web browser is much more feature-rich than the mobile app!