I've played a fair bit on both EU and NA rulesets as well as a bit on the new one so I wanted to give some thoughts.
Windiff vs Winlimit: I don't think this has made a practical difference in almost any games. Windiff rarely comes into play in EU as it is, and I think comebacks are a lot more common under the current NA ruleset by virtue of the map time being an hour. I personally don't think this matters hugely under current ruleset, but I think the unity ruleset probably should run with winlimit, as windiff makes it much more likely that things will go on forever (The only real problem with this ruleset imo).
Doughy
I agree that fundamentally this ruleset won't change a huge amount at a top level, beyond an increase in potential for comebacks. I think that the actual purpose of this ruleset is to create disincentives for doing a large number of small % plays. This is currently a fairly effective way to play, especially at any level below top prem/invite, because it doesn't require a huge amount of coordination and it's eventually effective. In your scenario, you can still go for your 5 low % plays, but with a 4 minute round timer you'd now have 48 seconds to coordinate each play from the moment you capture the second point and including respawns and rollouts. This is going to make these plays even lower % (or you get less of them) but will have little impact on a couple of moderate % plays that would take a while to set up normally.
In my opinion the low risk playstyle creates some of the least enjoyable TF2 both to watch and play, because the majority of players will be watching a door for sacs/counter sacs and waiting on a respawn timer during that time. This problem gets compounded even more when a team is up rounds and you're close to the end of map time, because then it's even more effective to do low risk plays and run out the clock. Imo a team losing to the clock is also a situation that should be avoided in TF2 where it can because it frequently just ends a closely contested game in the most anticlimactic way possible. This ruleset minimizes both of the things that I (and probably a lot of other people) find least interesting in the game and replaces them with midfights which are an interesting part of the game.