I wasn't expecting to see this case. I would say the issue is the lack of intake / exhaust fans. Those custom cards, unlike the blower style coolers or even the FE who exhaust a bit outside the case by itself, rely on fan cases to exhaust all the heat. The only fan I can see as intake seems blocked by some things in the front, and the only exhaust (not counting the PSU fan which acts as almost independant) is the only on the radiator. 
 
So to answer your question, it might but I wouldn't expect temps to lower after removing the backplate. Some backplate can indeed trap the heat, others that are more thoughts can help reduce the heat, but if your case isn't airflow friendly it won't matter much, sadly. 
 
Also, even if 78°C is a bit hot for me, you're still under 80°C which I consider the " No trespassing zone " (that's totally subjective since these GPU's can usually climb to 95 / 100°C before throttling / shutting down).

IWafflesI
I’m getting up in the 80c and higher range on my xc3 3090. They completely undersized the cooler on this thing.

There might be room for improvement there. A quick test to know if your case airflow isn't great should be to remove the side panel. If temperatures are (way) lower when you do the same things than when you get 80°C+, then your case might lack good airflow to be able to bring fresh air or to exhaust heat efficiently enough. And sometimes fan number doesn't necessarily means good airflow. 
 
My GTX 1080 FTW was above 80°C when gaming. I couldn't figure out why because I have 3x120mm intake fans that are 900rpm / 1500rpm (depending which mode I turn on / off) and 3 exhaust fans, a 140mm that goes around 800rpm on the back of the case and the other two being 120mm that ramp up accordingly to CPU temperature, from 800 to 1500 rpm. But then I removed the front panel of my Pure Base 500 (which is more about noise reduction and less about good airflow) and tried to maintain the same ambiant temperature, temperatures went from 80 / 85°C to 70 / 75°C max. Sure the 1080 is less powerful, but also got a smaller cooler with only two fans, and the fan curve is also a custom one I made for more silent gaming, default curves might probably get lower than 70°C.  
 
That's why many reviews will test cards on open airflow test bench, that way they are not limited by any case restriction and the only two factors are ambiant temperature and the card's cooler efficiency (fan profiles, cooler size, etc).

Yeah that case is brutal. Form over function. The cables clutter the airways. Eventually you’d want a more friendly case if possible as friend stated above me. You’d be surprised what a couple extra well placed fans can do for temps. Also these do get the budget cooler but even a great cooler won’t help if the card is choked.

FattysGoneWild
78c gaming with default fan profile. BUT, that back plate is holy crap! Extremely HOT and it has raised my cpu temps because of it. Being this is a new gpu. Will temps get better with the back plate? Couple pictures in link. 
 
https://imgur.com/a/c5mQrVv

- Buy a new case.  Preferably something with a mesh front.  
- Install system in new case
- Burn HP Omen case and scatter remains to the four corners of the earth

xxzenpunkxx
It does look like you could add an exhaust fan, to the back of the case.
Seems to be a open space for it right under your cpu radiator.
Might help take some of that heat out of your case.
 
 

 
Excuse the herp derp moment for myself. I am not understanding what you mean? 

I'm on my phone so I can't adress most of your questions but :
- should your cables be too short, there are extension cables that cost far less than a new PSU
- if you're open to look at videos I would suggest GamersNexus videos about best airflow cases. You can have all prices, from 60$ to 200$ so you don't need to ruin yourself.
Before buying, that might help you understand what you're looking for, what to avoid, what to expect, etc.

I'd suggest to put some heavy thoughts on that because even if you can still change later, it's still annoying to transfer components and redo cable management when changing case :p

doesnt look like you even have an EVGA card. so why is it posted to the EVGA forums?

gsrcrxsi
doesnt look like you even have an EVGA card. so why is it posted to the EVGA forums?

To be fair, if you look at some of the forum topics here, you'll see that a good chunk of the discussions aren't EVGA at all. lol.  I just saw a 12 page long thread about Kenmore Appliance Employee pricing.  OP's post is good as any here; at least it's PC related. 

gsrcrxsi
doesnt look like you even have an EVGA card. so why is it posted to the EVGA forums?

I have had EVGA cards in the past and posted a lot here. My first choice is always EVGA. But, they could not deliver (out of stock) the product at time of purchase for me.

Thanks. I decided to do a full case swap. I ordered the NZXT H510 Elite in white.

The h510 is almost as bad for thermal, stop going for look and get a mesh case like Lian Li lan cool 2 mesh or p500a or 4000d airflow. I own the 510 so I know what am talking about.

My 2080 would run 68-70c my 3080 runs 78-80.