Gravity pistol( as the carrier size will make things actually worse for the carrier)
Also that archeotech kind of pistols, which uses subatomic munitions.
Eh, not really. Grav-weaponry in WH40k still has limitations (you cannot, in fact, crush a whole aircraft carrier with one) and Volkite weaponry (if that is what you mean) is somehow similar to Meltas, but longer range, it mostly just makes people burt into flames and melts armour, so one shoot is not really going to do shit.
As for Tau and melee, there are few points.
First of all, Tau are in fact, in general, weaker psychically and have slower reaction speed than humans and Fire Warriors only overcome it by rigurous training and thanks to thousands of years of eugenics. So, Fire Warrior is an equivalent of a human Guardsman, which... isin't really that big achievment for a human. Humans can still be much, much stronger, while Fire Warriors are on their peak and yet they might have slightly worse reflexes.
Their eyesight is generally good but their pupils do not dilate, giving poorer depth perception and it takes them longer time to focus, so they automatically basically can't see shit in close combat. The high-tech super helmets do not really help, because they make all the downsides more down, though they do let them be better at range, which is... not bad, for a Tau.
Tau do not really have melee weaponry. Before Ethereals came they fought each other with melee and proably some kinds of bows, so they now think they're barbaric and a reminder of their violent (Tau were RIDICULOUSLY hostile fucks back then, possibly on par with Orks, even) past. And when they do, they're mostly ritual weapons - the bonding knives the squad leaders have are technically working weapons but using them in close combat with enemy and risking breaking it is... putting the honour of not only the leader in question but the whole squad at stake, which is something unthinkable for them. The Ethereals are obviously extempt because, while they do not really fight at all (the one time they did they all died and we got Farsight Enclaves), Tau are mind-boggling hypocrites who will accept anything they normally disagree with as long as the Ethereals do it.
Rollpgeek Theorm, which states that the Ethereals are exempt not because of their status but because of the artistic grace and skill of honor blade combat.
This.
I cannot stop laughing condescendingly.
Hey, Could someone give me odds that Ethereals are literally Eldar in fancy disguises?
Low. Very low. Lower than the odds that Ethereals are actually Necrontyr in fancy disguises.
Such as the pistol that fires basically black hole slugs.
Good luck packing an effective black-hole containment field into slugs that fit inside a pistol.
And fuck, you want to destroy the aircraft carrier, not reality in the dozen of kilometers around.