It depends on what your definition of "playing it safe" is - you should 100% start by playing as turtley as possible, and then from there look for holes where you don't need to turtle. It is always better to account for death to be around every corner when your party doesn't know the fight yet. You aren't the only one responsible for you, your healers have to watch your back and the party's back as well - being as sturdy as possible at the right times is key to allowing them to get comfortable with how damage flows in the fight. As the fight goes on, you both make adjustments for eachother to find the happy medium - back in Gordias this was to such a degree that both tanks and healers could go practically full time DPS because SE forgot that bosses needed to do damage. In Midas however, while there are plenty of times for tanks and healers to push DPS, it's not nearly as lenient as it was before.

Anyway, for the sake of your entire group making progress, it's better for you to play ultra safe and work in recklessness than to play ultra reckless and work in safety.

That said, there is an extent to playing safe. After you know that you don't need, say, tank stance for a section of the fight where you're only taking auto attacks, you shouldn't stick to staying in tank stance 5 pulls later. You should always be learning, always be adapting, always trying to work in new ways to keep your survivability high as well as your DPS output.

RE: We killed A7S right at enrage - this sounds like a case of a group that's inexperienced with raiding. Usually when you hear "let's focus on mechanics" and you're still having trouble with mechanics 10 pulls in then you're dealing with people who haven't raided before. The static I was in before it disbanded due to conflicting goals was realistically 5/8 people who were excellent players but had very little experience raiding. They pulled high tier DPS, but their inexperience with handling coordinated mechanics made it look really sloppy. As we kept pulling, though, they got better and better - had we not disbanded, I feel like my team could've been really good for the next tier, but you live and you learn.

I think that does play into optimization as well, though. Generally any group who's raided before will actually look into maximizing everyone's performance - while I didn't organize my raid team myself, I was the one calling out mechanics for them, and I would generally try to solve problems for other people when they weren't really aware of how to fix them. I would call out Mantra timing, LB timing, where certain mechanics would be happening, when we needed more DPS/healing, etc. Having that awareness was good for me to guide that team, but then you have to consider what it's like to have that knowledge on multiple members of your team - those members then working in tandem rather than just having one guy calling all the shots.

So. Yeah. Experience is key. More experienced groups will be more optimized. JP linkshell groups are a good source of this as they don't raid to compete in the world first footrace, but rather build off existing strategies and fine tune them as they don't feel rushed. If you look back at Lucrezia's style, they played like bulls - they forced their selves through mechanics in whatever way seemed possible, correct or not (you can look at their T11 prog for this). This is the style of a team focused on competing, more "what will get us through this" rather than "what would be the best way to handle this". The latter is what you'll get out of the slower JP groups, and that's why they usually come up with the best strategy (easy example is NA's Garuda EX strat vs JP's Garuda EX strat).