My man, listen to me. (TLDR AT THE END)
1) Stop refering as "Old AT". Its like when you are 45 years old and your back hurts and you say "BUT when I was 16 y.o. I was lifting weights non stop I was Mr Olympia !!", dude, if you can't acheive the same results, you just got worse for a variety of reasons, like ageing and getting slower reflexes and stuff, so accept it and stop refering to the past, because literally no one cares who you were.
I speak for experience, I play since Abyssal WoW, I went throught all the wipeouts (both gear and max rating, titles, mounts, legendary 2200 weapons...) and I recovered in few months (maybe years), I am currently 2k-2k3 with every class I play (all classes without pet basically), so again, you have no excuse to keep saying "OLD AT", after more than 5 years of playing HPal (2200+) I decided to try Hybrid spec like 2 months ago, and from relentless gear with 0 rating I am currently at 1950+ waiting for the flush for get the points for the helm.
2) SoloQ is indeed a hell, I gave up with my warrior (max rating 2k~, achieved before the merge with Ice and Lordaeron), because it's literally impossible to carry a 3s team as Warrior, at least for me. And since the merge with such realms, I just lose every single game as Warrior, despite me being full WF and capable to one shot people (I miss only shoulders and mourne). I don't have CoS, Vanish, some self heal, Warrior needs someone that full dispels and freedom him, otherwise its just a puppy to make fun of, specially vs casters, I stand there doing nothing but dying. Yes I have Shield Wall and Enraged Regeneration, but they have huge CDS and should be treated like a Paladin's Divine Shield = EMERGENCY.
If I keep getting slowed, rooted, controled and my healer can't even LoS a CC then what am I supposed to do as warrior, while my healer is 9 seonds in poly?
Druids , Paladins, Shamans, go behind a pillar and self heal, Rogue can CoS every minute, DK AMS, Hunter deterrence...and me? Shield Wall 5 minutes CD...ok you see the point I guess. I have only 1 fear as control that 99% of times gets trinketed istantly, or tremor if there is a Shaman, so I am literally defenseless.
But if you play Pala, Disci, Shaman, Lock, you will have a better time climbing the soloq with less skilled people.
3) 2v2 is even worse, don't trust ANYONE, and I say anyone, even the "nicest calm guy" you will ever find, it will ragequit after few loses, just dont play it. People who do 2v2 know each other for some reason or they are long time friends, but no 2v2 team made by 2 randoms will last more than 1700-1800 rating, it simply doesnt work, so forget that bracket.
Just for the info, I don't classify myself as a pro player, but if you wonder what is my situation right now, after 10+ years of playing its:
5x DPriest 2200-2300
2x Hpal 2100-2200
2x RDruid 2k~
1x Warrior 2000 (I have a 2100 on Icecrown but it was made in 2017 with 2v2)
2x Rogue 2100~
1x Hybrid Pala 1950 (currenytly playing)
Yes my reflexes got slower and my skill level is slighty worse, like I was used to Shadowmeld Blinds and Scatters, or SWD almost every Seduction, now I have to really concentrate to do that, but as you can see the overall ratings are kinda the same, and I don't need to say "OLD AT".
TLDR: Pick a suitable SQ class (Hpal/Elemental/Disci) and play that and see if you still have troubles.
Best regards