I think all the arguing about comparing between poker and chess is missing the bigger point - luck/randomness in hero pulls creates a huge disparity in raid difficulty. Yes a game like poker has incomplete information in a way that chess does not, but in poker, everyone has more or less the same tools available to them (cards, time playing, study materials, etc) to improve.
My main account had the following as it’s first four and five stars: richard, grimm, boldtusk, chao, melendor, grimm, tibertus, caedmon. Compare that to my alt account which got Boril, boril, kiril, li xiu, lil john x2, rigard, cyprian, gormek, melendor. the first account had a really easy time raiding and raided way beyond it’s own power for a long time. The second account really has to not worry about cups in order to raid in a timely manner.
I think that’s some of the frustration and why the sports/poker comparison doesn’t sit well with a lot of people. If you’re a baseball GM, you don’t randomly get assigned a bunch of players and end up with 12 outfielders and 0 catchers or first basemen. You get to choose who you draft and somewhat choose what free agents you sign (or more specifically you can choose which ones to target; you might not get them). But you don’t get that here, so it makes it harder for some teams to raid successfully without dropping cups. I’m not going to use the word “fair” or “unfair” since that seems to bring up a lot of emotions, but some heroes are designed for raiding, others for defense, (and others like cyprian for the trash bin).
So the ELO system itself works great at doing what it’s supposed to (ranking people over a long period of time with lots of matches), the catch here is that the inputs to each player’s team varies so greatly, yet the ranking system only ranks on one specific aspect of the game (raiding).
This is IMO only really a problem at lower and mid-team power/cup rankings, since once you get up higher, most people will have a large stable of 4-5* heroes (either via spending money, training camps, both, or just plugging along for months).