Yeah, an untreated room will be off, but there are basic "treatments" you can do via geometry and speaker placement that can make a dramatic difference. You don't have to cover your walls with insulation panels and have bass traps in your corners, as long as you place your speakers in a symmetrical position (avoid corners if you can) and have some sort of diffusion around+behind you (bookshelves or any other furniture that breaks up incoming sound waves into a relatively random/uneven dispersion pattern so you don't have too much flutter and reflections).
Having accurate bass representation in a home studio will be impossible 99% of the time, and while a couch does help a little bit you'll still find yourself in the position to compensate in every mix, just be wary of the crossover frequencies between your sub and speakers.
As PRYZM said, regardless of how flat a speaker is, your room will unflatten it, so follow some basic setup rules to get the most out of them:
Have your speakers pointing down the length of the room if possible.
(most important rule for home studios I think) Maintain an equilateral triangle between your ears and the speakers. Have them pointing at your ears and be the same distance from each other as one is to your head.
Try not to have bare flat walls to your left or right (immediate location plus 1-2 feet behind you, wherever you approximate the sound from the speakers hitting the wall first)
Don't have your back up against an immediate wall, the longer the space between your back then wall behind it, the better bass response you'll get.
There are debates about what is the best way to set up speakers, but what there's no real debate about is that haphazardly placing your desk+speakers in any room is not the best idea, so try to follow as many setup guidelines as you can, even if you can only do one of those, it'll be a huge difference between having none.
The Presonus Eris 3.5 in that graph are not flat in the least. There's a pretty large 8dB resonant peak at about 110hz and a large 9dB boost between 1khz-1.7khz, they're designed more for listening than mixing, so you'll have to watch your bass mixing and the very important 1khz area (between 1khz-2khz is where a lot of speakers of all price levels tend to vary a bit). If you want to test, load a simple sine wave patch and play B2, and then play a D4, you should hear a difference in level.