I am not a pro but I have recently received great advice from people on ELO deck building, and as a result I got to 1,234 ELO in a couple days. Please, if you feel that I have no authority on the matter, disregard what I have to say

From what I can tell, your deck lacks a lot of utility. A successful ELO deck, no matter what clan or clans you construct it from, seems to follow one very basic rule:

Be prepared to lose two rounds in a game.

This means having a lot of utility available. SoA, SoB, DR, Defeat: abilities and walls. If you look at Berzerk / Uppers public presets for ELO, almost all the successful ones that have reached 1,300 ELO or more feature Elvis (SoA), Lola (Defeat), Melanie (wall) and either Samantha or Wendel (SoA). Other frequent appearances are Rubie (SoA) and Maurice (DR).

These cards allow you to answer your opponent's threats in different situations: mitigate damage, neutralize a pesky ability, make your opponent overpill to beat you, make it very hard for your opponent to stop your attack if their rely on card abilities, etc.

Lola, Maurice, Jose Star, and Miho is a good foundation. The rest of the deck is alternative choice cards taking the place of staples. Cortez is a good card to build a 2hko deck around though so if you wanna go with a 5/4/4/3/3/2/2/2 deck I'd suggest Uma to Melanie, Jonas to Rubie, and Wayne Stark to Kazayan or Nellie.

Jonas terrible, Wayne Stark terrible, Cortez terrible, Uma terrible of course you are not doing well. well you ARE strong against SoA but thats pretty much it. not to mention you do not have soa at all.

as mentioned if you are using berserk Elvis is a MUST (otherwise dont use berserk) and Melanie is VERY much preferrable... Sprinter is really good imo. Uma is overrated. Cortez just sell that crap.

Wayne Stark is plain terrible 7/5 is weaker than Oxen if no SoA/SoB prescence.. Nellie and Kazayan WAY better. Rubie is so godo as well. Jonas... are you high?!

haha sorry being a bit offensive... but heres a deck suggestion.

Elvis Sprinter Melanie Lola Rubie Oxen Kazayan Jose Star

Cortez isn't as bad as some make him out to be. He opens up a lot of two hit ko options. Miho is also a great round winner when not facing SoA and deals terrific damage for a two star. So although they aren't staples they are very useable candidates. Up to you really. Elvis, Sprinter, Nellie makes a nasty trio though.

I like the clan combination. Nice idea to have Bezerk pull in the life gap and Uppers to waste opponent pills. The characters themselves aren't that dynamic though.

It seems like another problem is that the deck is too top heavy. This wouldn't be as much of a problem if the 5* can really carry that victory like a Beeboy or a Askai, but Cortez just can't win his round as easily as those if you happen to draw him with 3 lower star cards. And if he loses his round, you may have an extremely hard time pulling in the dmg needed even if you win the other 3. Same with Maurice and Wayne Stark... perfectly fine cards on their own but they aren't exceptional enough to spend precious star space on.

Definitely lose Uma, Jonas and Wayne Stark. The former two are extremely difficult to win with (first you gotta trigger their abilities, then win with them in their round when they don't even have 8 power or a att manipulation ability). Wayne just takes up 4 stars that could be spent on much better cards.

Wayne Stark to Dorian/Hefty/Herman
Cortez to splinter/Revok
Miho to Melanie
then
Jonas to Wendel/Samantha/Gail Ld
or
Jonas to Harold
and Uma to Bernie

Lol no Gail Ld is terrible i would rather use Wendel for that extra SoA/Jose Star

Gail Ld is by no means terrible, i have snuck in a 6 damage KO easily, she is preference, by far she can cause the most damage as a 2* and can help with 2hko next to some of your Berzerk cards and Herman if you chose him over the other 5 star cards.
alot of players prefer Wendel cause he seems more useful as a 2 star, i would agree except for a few things. hes courage based and in elo a LOT of decks run cards with "stop:" abilities meaning they are looking for that Wendel to open or hit in with courage so they can smack you with (just for example as a commonly use card) Karen boom half your health gone with 3-4 pillz thats gotta Sting. vs gail who after winning the prior round could act as a HUGE bluff (your opp tries to block a potential 2hko and overpillz leaving him/her open for attack) or you can actually sneak in and pull off the 2hko if your faceing the right opponent or if your opponent pillz alot and still loses (say vs Herman) you can use her 6 power and -10 atk to maybe get the damage in with your opponent unable to stop it
so as you can see its a matter of opinion but to call Gail Ld terrible is a great overstatement and undervalue of a perfectly solid playable 2 star for the Uppers (about half their 2 stars really are unplayable)