I did eventually finish this map on maddening! But I had to reload to an earlier chapter (right after 7 when you get Alcryst) to redistribute my master seal in order to do so. I went in with Alear (promoted), Chloe, Celine, Citrinne, Vander, Louis, Framme, and Alcryst (promoted). I also had to buy a strength tonic for Alcryst, which pushed up his STR enough to oneshot all the dragons with a Steel Bow +2. The key to this map for me was getting an archer to that oneshot threshold. Once Alcryst could oneshot the dragons it was much more doable.
The way I did the map was to not even go up the middle alleyway at all after the reinforcements waves stop spawning. I used Alear as a dodge tank and Louis (rotating him out for Chloe when mages spawned) to protect the other units. You can stack them all at the bottom of the map behind Alear and Louis so only ranged units can hit anyone else. Alcryst shoots a dragon every spawn wave. Alear + Chloe or Louis kill the other dragon that spawns every wave. The rest of the units kill whatever else spawns.
The waves DO eventually stop! At around turn 35 or so? The final wave is 3 dragons, that's when you'll know it's done.
The rest of the map after the reinforcements are cleared is much easier. Just proceed through it safely making sure to pull only a few mobs at a time.
What I was not prepared for was Tiki and her friends charging for me as soon as I stepped on the second seal. As I was out of position, I was forced to blow Marth's Lodestone rush sub-optimally, which meant I didn't have it for Tiki. This led to Citrinne getting oneshot by her (I was off by 2 damage!!!! grrr), but honestly I was fine with that. RIP Citrinne, I got you last chapter and you already died.
Next time, now that I know Tiki will charge me, I'm pretty sure I can get through it with no one dying. But yeah this map was definitely a doozy for me.
Also, you can get the silver card on the map without warp by sending a unit around the right side. I did this with Vander after the waves of reinforcements stopped. But he had to stay there for the rest of the map because a dragon would kill him through the wall if I brought him back to fight Tiki.
This map scales to above your level, so you cannot outlevel it. I haven't tried doing it late in a run yet, but I honestly think maybe doing it early (like, directly after it appears and you have Alcryst), might be the best move, as that's what let me succeed this time. At some point with higher levels, Tiki gets more revive stones and that's...not something I want to deal with lol.