I haven't played Kingdom Rush or Clash Royale much (though I did for quite testing purposes -- one of the companies I worked for used those two as inspiration for their own art style). I have sunk many hours into Bloons.
I wanted to allow for people to create their own paths to defend as it's another avenue for possible strategic thinking. Do I do long stretches to maximize distance, do I do lots of cut backs to give towers more chances to hit the same attacker, etc.
I didn't realize how lacking the detail was on how the paths were built until I saw the feedback on it, and then, when I thought about it, realized I didn't really know myself. If I'd taken a few minutes to draw a simple sketch, I'd probably have picked it up.
Flight was the power that made me decide both players would see the other's attacker-waves being built, so you'd know you might need something that was anti-air. However, I think if I were to pursue creating this game, flight and other 'rule-breaking' abilities would not be in an MVP or even a version one. I love the complexity of some TD games and would like to include stealth, lane-hopping, flight, de-powering defenders, etc., as they force you to think about defense differently.
> What kinds of map design features will prevent a player from just building "the shortest path" to the base each match to make sure their troops consistently get there first?
You're building the path to your own base, so you don't want the shortest path. If that wasn't clear, I definitely need to improve that part of the document.
You first decide what kind of pathing you want to build, to hinder the enemy attackers. Then you see the path they've built for you on their territory and they see the one you built. Then you start choosing attacker-units and defender units.
"Oh, he has lots of long straight-a-ways, I should use the attackers that speed up when going straight."
"Oh, he's got the big tanky attackers, I need to get a tower that reduces armor or ignores it or something, let's see what I have ..."
You place your towers, while trying to keep an eye on what the opponent is building, both for attackers and defenders, and adjusting accordingly. I don't think I want to allow for undoing a choice once made, or we'll have people who's entire strategy is to swap out things in the last second.
After I submitted, I was thinking some tutorial maps may have a preset path, to help explain those strategies (long paths are good for x, windy ones for y, etc.). But the build-your-own-path could be optional overall.
I can see lots of room for later evolution in a game like this. Attackers that stun Defenders (and vice versa), special abilities that players can use during the battle (though it'd be a bit less of an auto-battler then) like bombs or damage and speed boosts for units.
Thanks for the feedback!