If a player is GM and their friends are GMs, then how is it abuse? They're all already GMs. Acquiring GM when you're already a GM isn't an abuse. Beating diamond players as a GM isn't abuse. Therefore, your claim of abuse is rooted in the "smurfing" aspect.
It's only abuse if a person who doesn't belong in GM is reaching GM by queueing with diamonds. Which very well may happen. I'm sure there's a few master players who've reached GM by queueing with diamond friends (even if those diamond friends weren't GM smurfs). Or a few diamonds who hit masters.
That's why I suggested that it's only "abusive" towards the diamond players who are losing mmr/ranked points against GM-smurfs. But that's a "smurfing problem", not a "grouping with other GMs" or "GMs beating diamond players" problem.
However, smurfing and grouping are not automatically abuse, especially not because people who are already GMs are beating players who they're objectively better than, or because they're reaching a rank they already deserve... simply because you don't like it. It's the nature of these types of systems, which is why I went on at length about how these types of problems occur every match, at every rank, whether you're against GMs and/or grouped or not.
I agree that diamond players shouldn't be losing MMR/rank points because they were paired against diamond GM-smurfs. And I agree that it feels abusive. But that isn't the issue being isolated by you or OP, and it's not "abuse". It's function of both how Blizzard chose to design the system and how ELO-derived systems operate implicitly under the circumstances of multiplayer MOBA games.
No player, at any rank, smurf or not, group or not, should be losing or gaining MMR/rank points that they don't deserve. However, often 8 players experience a false negative or false positive every match they play. And Every one of those false negatives and false positives results in corresponding errors in 8 additional matches to 8x as many players stemming from the first, until you get to the point where nobody's MMR is truly accurate.
In order to fix this issue, you need to take personal performance into consideration. You aren't going to stop smurfs and you aren't going to stop grouping (unless blizzard makes it solo-queue only). Best case scenario, you make the groups as small as possible with the smallest possible variance between group members, and the "abuse" you claim continues just to a smaller degree. So instead, the system needs to isolate players who are overperforming at their respective MMR, and adjust them quickly and accordingly (even if the adjustment isn't perfect). As a result, those diamond GM-smurfs (or any smurf) wouldn't be able to get away with smurfing for more than a few games, because their outsized impact at their respective MMR would no longer be ignored by the system. They'd play 1 or 2 games as a diamond Smurf and instantly be adjusted towards masters/gm.
Anyways, if you think I "[misread]" your first post then there's probably no reason to continue. My responses certainly aren't going to become clearer as I attempt to explain every implicit detail.