I totaly agree with your "hammer-comparisson". No Doubt about that.
That "tactical variety" (maybe this expression does not get to the exact point I mean) should be a bad idea, I cannot agree. Having many options does not mean, using them necessarily all (at the same time) making an uncoordinated mass out of your fleet. But it's always good to have lot of possibilities to choose from to optimize your fleets eficiency.
Mayba you're right and squadroning is the right ting HERE, becaus Marines simpley need it.
I still think it's a kind of double edged sword. Especially when it comes to brace. If (or better when) our opponent focusses his fire on one of your strike cruisers you'd loose it quite quickley if you do not brace. (But bracing has a massiv effekt on your firepower when using a squadron).
And as mentioned before: Lock on. If it happens that you could go on lock on with some of the ships but others would need the turn to get in range to the target,...what to do? lock on? loosing a ships firepower, or turn loosing lock on on others,...(simmilar if AAF, CTNH would be needed on single ships)
But I'm afraid we're getting to far from the topic to "usefullnes of squadrons"
Back to the Marines vs. Tau topic: I'd try to get quite close the Tau making it harder for him to use is firepower concentrated at his front arcs.