The absolute definition of Pay to Win boss 

I think Dracula T, Shuijing MB is better for her, since she doesn't crit. The other things yea, you can get away with not using their signature gear, but you'd want at least better support sets, not to mention Gilded Librae only gives elemental dmg, not phys. Phys also the most expensive team to build, since it needs Senti, but I have seen this team clear with the same team you used, just with a better support set on bronya. I think I've seen her able to use Tesla/Mei/Newton, all of which can be free from exchange shop, just takes time to farm the stigma resonance from open world. I've seen Griseo use the Theresa Origins set, since Marco Polo isn't a support set, and it was pretty good. Red lotus and above is expensive, but I think for certain content you can use farmable stuff, it's just very expensive/time taking stuff to get. Agony is doable with just about anything though lol

full Dracula simply doesnt work on sus. best farmable i suppose are Dracula T Shuijing MB/Dirac MB. MarcoPolo on Griseo is also very questionable, she's a support, not a dps. also you can farm CH (willpower thing) and get gustav klimt TM newt B (exch shop), and griseo can do Hekate Gloom (exch shop) and Glut/Mei/Newt

your unspent stamina says you dont play much. not to be rude, but can you show if youre f2p and spend on ridiculous things like outfit supplies? you should be focusing on gearing your valks with their signature gears. theres a ton of f2p players who retain redlotus and nirvana simply by having their priorities for their accounts in place. cant really agree with the P2W cop out if you arent maintaining your account properly. I beat this boss with HoS 4/4 S0 Gris 0/4 S0 and Sus 1/4 using ely TB charles M and her weapon lv35. the boss can be beaten, but as usual people will always have some excuse.