That is another purpose, but to me the more important one was having a distinctive goal that you could see from a distance and strive for. That wouldn't work as well with mountains because they're less distinct, ("which mountains are the landmark ones?") and the smaller size of the towers makes it easier to arrange neat challenges around their base for the player to overcome.

Well I'm arguing off the basis of skimming the discussion you were having with him ... and on that front, didn't he say he'd rather the map be revealed by your location proportional to it (sort of like "if I stand in this area and x town is 25 feet away it will be marked on the map")? If that's the case you wouldn't even need a "reveal the map" tower or mountain like you say. 

Towers are not exactly the most interesting goal to strive for ...  

Either way I like how Towers are implemented in BOTW, I don't really care either way if they go, although they might not fit the setting or story of next Zelda.

Newsweek (of all publications) has an exclusive preview of the upcoming The Legend of Zelda: Breath of the Wild—Creating a Champion.

"Creating a Champion spans 424 pages, and includes material from both the game’s DLC packs. The book features 296 pages of design and concept artwork, commentary from the creators, a 55-page comprehensive history of Hyrule, and nearly 50 pages of official illustrations and sketches by Takumi Wada, the series’ lead illustrator since 2011’s Skyward Sword. The volume also includes interviews with key members of the development team, such as Wada, Hidemaro Fujibayashi, Satoru Takizawa and Eiji Aonuma."

Source

Come on, Wind Waker? Nah, my dude. That game is actual crap - and by actual crap, I mean only pretty good.

Look, I love Wind Waker as much as the next guy, but... looking at it objectively, it does nothing very well. The dungeons are all really boring, as are nearly all the bosses. The game is consistently very easy but extends its running time with loads upon loads of padding. Exploring just in general isn't very fun because of how long it takes to get anywhere, and you rarely find anything meaningful. I could list problems on and on. The reality is, there's only one thing Wind Waker does well, and that's the atmosphere - but it does it so exceptionally well that it pretty much sells you on the whole game. You can't help but happily play through its mediocre content because the visuals and music, as well as the story and characters, are so great that they create this 'magic' feeling unlike most other games. It's taken me long enough to figure this out, of course. When I first played through the game I didn't have this clear of a view on it, but nowadays I can see that, objectively, it's quite an average Zelda game.

Conversely, A Link to the Past is probably the best Zelda along with Breath of the Wild from an objective point of view. Both strike a good balance between free exploration and linearity, allowing the players loads of freedom to explore while not becoming overwhelming or too difficult. Both have loads of content, and even if that content is focused on different areas in each of them, it is all very high quality. But most importantly, both of them have very engaging overworlds with loads of secrets and interesting things to find.

Neither of these is my favorite, by the way - but I guess many here would know that.