You'll never reach full potential with just one element. Sure, you can clear things, but there will be content that makes you wish you spent a little more time and effort on a certain team. And if your team and grid is maxed or nearly maxed out, the only way to increase your potential is through element advantage, which you will only have against one other element.
Also, a good team with a good grid + element advantage, will always outpreform a 'perfect team' + a good grid, while fighting off-element.
There's no need to put all of your eggs in one basket, especially with the consideration of M tickets. Focusing on one team just makes the game harder for yourself, because most off-element content is a pain for you to deal with, which is the only reason why farming for all elements at the same time sounds like a full-time job and utterly pointless. If all of your teams have been taken care of, even stuff like Stage 4 accessory quests isn't difficult to do on each of them. I know some people who take about 20+ mintues on Stage 4 due to having to use teams with weaker grids. Meanwhile, stage 4 took my thunder and water teams about 8 - 9 minutes to clear--while watching animations. Neither of which are my strongest teams. In fact, water is one of my weakest elements.
Let's not forget that having several good teams would also speed up and lessen the time it takes to strengthen your other elements.
As for the materials--with the new gem quests--it's now a waste to spend your AP on standard/expert disaster raids. All you need is an alt for raids to blow BP on. Most of the disaster assaults are already being cycled out and you don't even need the help of SR fodder anymore. With a decent rank, and letting your AP nearly cap out before each gem quest--plus 2 HEs--can net you close to 80k gems. And provided you sell back Ns and R eidolons, 80k is usually enough to do 100 x10 gem pulls. You can easily manage to do this every day, as long as it fits your schedule. By doing 100 x10 gems pulls everyday, you get so much R weapons that it allows you to greatly accelerate your SL enhancment progress.
By stacking several R weapons on top of each other to SL 2, you can easily get an SSR from SL 11 to SL 20. Before, this would have been unwise, but with 100 gem pulls everyday, there's just no point in trying to be frugal with R weapon fodder. Counting all the weapons I own and use for my grids, there's about 680 SLs--of which I've currently enhanced a total of around 553. So 553/680 SLs completed thus far. If I continue my pace of 100 gem pulls a day, I estimate I will have completely maxed out my total SLs within a month's time (counting future event weapons within that time).
It sounds like a lot of work, and something that would sink tons of HEs, but it really isn't. Let's also not forget that before long, we'll be getting HEs from gem pulls, so it's not going to be a limited resource.
And once again this discussion was never about max damage potential. It's quite obvious that a mono SSR assault grid is one of the best ways to do that. But that's endgame, and we haven't reached that point. This discussion is about utility. It's about which grid type builds into endgame better, which grid type handles all events the best. A comparison between which grid type is more versatile and less painful.