Impressiveā¦ but saying itās all about good counters is a great understatement 
you need to be pro player with lots of resources to play like this. if you would give those counters to some rookie player - he would probably delete them to make place for ārealā pokemons 
it is something similar to what I did in previous century when playing Tomb Raider - after some time I was bored and I made a challenge for myself - play whole game without using med kits and with shooting only basic pistols - it was fun 
Today I almost gave up when fighting Arlo (Scyther-Gyrados-Scizor) - but I finally beat him with Golem-Machamp-Magmortar. GOGub was not very helpful here as it assumes player has access to super duper legendary/rare pokemons and have zillion rare candies to power them up completely.
I had numerous goes Arlo last night as well.
Mine had:
Scyther
Crobat
Scizor
Ended up finally getting the job done with:
Golem -Rock Throw/Stone Edge
Tyranitar -Smack Down/Stone Edge
Entei -Fire Spin/Overheat.
All are L40 Maxed and 100% IV
Iāve now set one of my 98% Golems up with Rock Blast.
My Melmetal has the duel charge moves (a power up accident) recommend in the Go Hub guide but it was in a Gym and is currently only at L32
Flame Thrower I think is an exclusive move from the Raid day. Iāve got it on a L20 98% that Iām not sure how much value I would get from the 250K Dust required (I have the Candy)
My L40 98% Raikou was useless against Crobat as it never even got off Wild Charge before fainting.
Maybe. I havent got a chance to try yet myself since ive been ill since this got released. Anxious to try it though. A challenge in this game would be refreshing.
I faced the same Arloās line up as @NotanotherKangaskhan, my line up was Sky Attack Moltres which resists Fury Cutter from Scyther, Raikou and Blast Burn Blaziken. My Blaziken was at full health when facing Scizor, one Blast Burn KOed it. I did not use Entei because of its one-bar charge move.
Iāve done 5 rocket leader battles, only one I had trouble with is Arlo with Scyther, Magnezone and Dragonite, Scyther knew fury cutter so my t-tar kept getting destroyed. Ended up using Rhyperior -smack down, earthquake and surf
T-tar- smackdown and stone edge
And my hundo latios with dragon breath and dragon claw.
Thought my wife would struggle with the leaders since Iāve had to redo every leader battle, she did it no problem only lost one mon (she went up against Cliff: meowth, flygon, t-tar) she used Golem and metagross and had a gardevior as her third mon.
I see Giovanni is finally releasedā¦ looks easier than his leadersā¦Hopefully he will have not only Articuno - as I miss the other two birds in my dex
Try the Research Breaktroughs. They can give your two missing birds as well.
This is where I got my first Articuno from
Yeah, sooner or later I should be happyā¦
Thinking about Giovanniā¦ if this supposed to be repeating monthly task - it would make sense to give different legendary pokemon every timeā¦ for now there are reports of 3 birds listed as shadow legendariesā¦ so it would be first three monthsā¦ laterā¦ maybe something else. Hope I am right
Had Clif last night.
Meowth
Flygon
Tyranitar
That was a pice of cake
I just started stage 3 this morning. Still have to battle 4 grunts and win 2 more Great League Trainer battles.
Just got to stage 3 tonight.
Also fought my first Rocket Leader tonight: Sierra. Thought it was fun, to be honest. Not overly difficult if you have the right Pokemon, but still takes a little strategy.
I didnāt even waste my time fighting the leaders until I get to that stage.
I wasnāt going to, but I was curious. lol
Originally I wasnāt going to do them till I got to the stage but I really wanted to get some shadow mons (potentially shiny) and the fact that itās a repeatable task
3 days, 12 decoys - still no Giowanniā¦but I got my first Shadow Lapras
Faced Cliff for the first time tonight and got my tail kicked both times. Then I realized I should purify a few more PokƩmon to finish this stage before I beat him.
Got him finally - at 15th encounter 
Problem was Rhydon - as it just did not bothered with my Kyogre/Swampertā¦
But very well responded to Torterra - so I ended up with Matchamp/Torterra/Aggron
I beat Cliff yesterday, but Arlo kicked my butt twice on Thursday.
Iām still stuck on Stage 2 Purify 15 (only 2 so far) as I refuse to drop anymore than the 1K minimum to Purify junk.
Canāt find a Rat, Bat, Weedle or Magikarp to move things along. Iām getting nothing but Porygon and Bulbasaur with the odd other one thrown in.