I've worked out a team composition that counters the flakspire army, but it's very demanding in the way that
1) Captains need to be decently skilled and need to put their trust into you as much to change loadouts
2) Their crew must also be good-ish, especially the gunners
The problem with 4flakspire is it forces the other team to go for trickier strategies, they're snipers AND close range weapons, very much similiar to how Ducks used to win with their Metajunkers, except they're far less mobile and more responsive to charging ships.
Which then brings up the inevitable conclusion that they're countered by sniper ships.
Now, I was lucky to join in with my clanbuddies as allies and one pilot who listened to us, so we ended up taking two sniper galleons, one hwachafish (Ikuto's very nervous to pilot anything but a Fish and Pyra :c) and a Hades-lumber spire. Sadly, my spire was one of the reasons we lost that game because Rydrs focused it down whenever they could. However, even so Galleons were a fairly good substitute for countering the spires due to their fast disable/kill potential. If the pilots refuse to take drouge and go with claw to increase their chances agains't brawlers then they'll be more vulnerable to galleons, if the pilots take drouge then you can potentially have a chance against them with something like a hwachafish with banshee on the side just for the sake of supporting your allies. Chute vent should also be useful if you're the brawl/support ship. While flaks have average arcs on both vertical angles, Rydrs' strategy is to fly high and fly together to confuse their enemies and start firing from the max range, so you have plenty of room to get out of their arcs below if they decide to focus you down. Make sure to tap that thing hard for a good 2-3 seconds. You can even try sacrificing claw for Hydro, as you won't have a lot of time to brawl with those ships. However, back to the galleons, while they can tank and kill spires good, Rydrs can simply overheat the shite out of their guns and get much more accurate hits on them with HF over ranges.
Which then brings up junker. Thin hull profile + fairly high armor health, with flakspire around your hull health won't matter in the least bit, which junker gives up in exchange for armor and thus makes a semi-perfect counter. But no ordinary Metajunker, fighting agains't 4 flak spires is all about fast kills, thinning their numbers before they do the same to you. So double arts won't work not only because they're not the fastest killers around, but because disables won't matter with 15 more flaks shooting at you after you disable one. Instead I would suggest a hades-flak broadside, with either a flak front for trifectas or a flare gun for support (Red Spulcher's clouds give brawling teams on blue side a good chance agains't snipers, fairly balanced for such a large map.)
So to break down, the 3 most reliable builds agains't Rydrs' not-so-fearsome team composition on Fridays are:
1 - Meta Galleon
2 - Hades Flak Flak Junker
3 - Hwachafish with banshee side (to some extent, optional ship choice)
Meta Galleon and Junker do the killing, Hwachafish gets in semi-brawling range at the right times and uses hwacha's rapid clip release to unleash hull damage/disable all the flaks on a ship at once in brawling range and support hull damage with the banshees.
However, there are a few problems. As I've listed above, sniper ships like these depend more on crew's accuracy than your piloting most of the time, so if you fall in with a bunch of novices you've already lost the match. And this build also assumes the Rydrs will come at you for the whole game, and if they suddenly stop you shouldn't extend too far - the closer you are to their spawn the more time it'll take for your slow-ish ships (junker and galleon) to reposition and reorganize on death, which will mean Rydrs will most certainly focus the galleons first at that point, which means your team must ensure the Galleon stays a bit behind everyone else and is protected from the focus spire. It also requires active comms from the captains to focus down ships as soon as they come in- Plus they can kill faster than the spires if they focus down all at once, all-flaks can be redundant in most cases. Microphones are recommended among captains because if you simply try comitting to focusing one ship down Rydrs will catch on and constantly shift the ship leading the charge to get you to overextend and gain a few free kills.
Ladies and gentlemen, this has been Keb reveals confidential information: The Musical , we (I mean, I.) hope you enjoyed the read from someone who just happened to take part in setting the current Rydr death record on Iron fork. And to rest of you Rydrs, from now on, good luck!