I put 'pages of bot teams' in quotes because of Plarium's claim that they weren't bots - not that they ever gave a serious explanation of what they were instead. You didn't mention those words, but clearly it was what you were referring to when you talked about players being given Arbiter for free. And I was assuming that you weren't around at the time, since you didn't seem to include yourself in the people who got all those free wins - reading this reply now, seems you did get them but just not long enough to unlock Arbi, which I can imagine is very frustrating.
As for players having the GH completed due to that, it actually sounds like you didn't miss all that much of the free wins period, most people got probably a few thousand medals like you, maybe somewhat more but not like tens of thousands, unless they were whaling hard on arena refills. As you can see in forum posts or youtube videos from back then, arena was super hard for most of 2020 as well, it was only the final 3-4 months that suddenly it became ludicrously easy.
Not sure what you mean by 'it's not a flat value'. We're talking 11 percent of the champion's base speed, the difference between HK's aura and Arbi's, so depending on what the champion's base speed is, that's approximately between 10 and 12 speed as I wrote.
You are absolutely right about the speed requirements in arena becoming crazy, but what I'm saying is, Arbi's not the biggest problem there, gear is. If you had made that 240 speed team in October that you refer to, with HK plus Seeker, and then you switched in Arbi instead, you'd only gain 10-12 speed from her aura - all the rest of the extra speed needed has to come from gear. Though Trevor is right that if you use Arbi *and* Seeker or some other TM increase champion, the difference is bigger.
I'm indeed not in S4/G1, I'm in G4. The large majority of teams that I see, as you'd expect, is led by Arbi or Lyss - against Lyss I'm even more likely to lose the speed race than against Arbi, though of course Lyss can't revive so it's a different fight. But the teams with different leads aren't necessarily easier. There's Tormin leads, for instance - certainly possible to beat him with a typical speed nuke team, but only with a lot of good RNG/luck to avoid his freezes, so you may have to try two or three times for one win. Duchess leads - you may be faster and attack first, but if she's properly built, you can still easily lose regardless. Siphi leads - you can imagine.