Warning, very long reply ahead 
There definitely has been a bunch of cheating going on the last couple of months. Roping bots have been around since the introduction of the Rewards Track (at least that’s when they bexame very prominent) , but those are basically free wins, so not really a big problem. As for game altering bugs, notably the last 2 days the spell Bioluminescence was granting +2 spell power to all your minions instead of +1, so people absolutely flocked to Burn Shaman to take advantage of the bug.
Likewise, there was a bug with another card (blanking on the name atm) that was supposed to buff minions in your deck and it was also working on hero cards and weapons. If you got that down before drawing your hero card, you’d have a permanent attack value for the rest of the game after playing the hero. I think that was a Rogue class card, but I’m a little hazy on the details; I’ve been swamped with my job and haven’t played as much as normal in the last few days.
There were also big problems for a while earlier with Queen Azshara being played with Brann, and similarly with Nellie. The bug would make your opponent unable to act during their turn, or skip their turn completely, and the only way to get unbugged was a full game restart. In many cases, I’m sure that some people were completely unaware of the bugs, but there were many people who were and took advantage of the situation. There have been other bugs like that in the past (the newer version of Ysera comes to mind), but 2 in Journey to the Sunken City expansion and 2 in the Throne of Tides miniset is quite atypical and problematic.
Both bugs were hotfixed yesterday, so I’ll note that if you look at HSReplay to get an idea of what is best since the launch of the miniset, it’s probably going to be inaccurate given that. After a couple of days, it should normalize out.
I’d also note that having a collection of 260 cards does put you firmly in rookie territory, though. Each expansion is around 140 cards, and the minisets tend to be 35 cards. I don’t have every card, but I have a relatively full collection of everything after Un’goro, and HSR says I’m at 7000/7723 cards. Notably, the 2022 Core Set, which is free to all players, contains 250 cards. So, either 1) your collection count is off, or 2) you only have 10 cards that weren’t given for free, or 3) you haven’t unlocked all the Core cards (by hitting level 10 on each hero, which is completely doable in Practice Mode against the Innkeeper, rather than versus players). I suspect it’s probably a combination of 1 & 3.
If 3 is involved, I highly recommend completing that requirement. You will not only get all of the 2022 Core cards unlocked, but you’ll also earn experience towards the Rewards track, which can give you cards or card packs. You won’t get as much experience as you would against another player (and definitely not as much as beating another player), but it’ll still add up while you get more Core cards. So, 2 birds, 1 stone. And once you’ve hit level 10 across all classes, you’ll have satisfied the requirement not just for 2022’s Core Set, but every year afterwards. Well, until they add a new class, but that has only happened once since the game launched, when Demon Hunter was introduced in 2020. They will likely add Monk or Deathknight at some point, but it’s pretty much guaranteed to happen in the first expansion of a year, when set rotation occurs. So, it’s extremely unlikely until 2023 at the earliest, and likely further out. In any case, once that happens, you will just need to level up that class and youre back to a full Core set again.
Hopefully that provides a bit more context and has some information that will help you as you progress. If anything I said is confusing, just reply to this comment so that I get a notification, and I’ll clarify things. I’ll try to keep an eye on the thread in general, but the notifications definitely help remind me. (And if I miss it, hopefully some of the other helpful people around will answer as well.)