I'm not spinning anything, this is literally what you just said. 25% of the group carries the rest = good; 60% of the group required to work = toxic. To me these numbers not only reek of being arbitrary and pertaining only to content for 40+ players, it also makes it look like you want to turn content into a free ride, whether that is your intention or not.
Lol. Sorry for trying to get you back on topic!
There are two separate conversations here. 1. "Purely mechanics-driven battles aren't fun for anybody" and 2. "Content that requires high levels of execution is too hard for most players." It's possible to have a purely mechanics driven battle that is so easy that everyone can beat it, but this would not solve one of the overarching problems. It's also possible to remove all mechanics and make a battle a gear faceroll, but this also does not solve one of the overarching problems. Your suggestions aren't doing many favors for EITHER side, and certainly not both.
Twintania is already much easier with the availability of i100/110 gear and the echo buff. She's just not "fun" to some people because they still have to respond to a number of unforgiving mechanics. Now, should 100% of players be able to kill Twin today? Some posters in this thread seem to think yes. Yoshi says no. If they wanted 100% of players to have downed Twintania today, they would have continued to increase the echo buff, which has been proven effective in increasing the number of players who kill her. So basically, what you're asking for here already exists. You just want it to happen faster than the Producer does.
Let me ask you this. Can you imagine people losing to Twin with a 500% echo buff? They'd pretty much have to be trying to lose, right? Now, would you want that much power bloat to be in the game already?
Instead of looking for ways to allow mainstream players to clear all content the day it's released, maybe it would be better to look for ways to make fights more fun for mainstream players without trivializing player skill and/or making victory RNG dependent, within the confines of the current battle system.