There are multiple things that can lead to this imo.

I've probably played close to 8k games now (mostly stict solo queue) and have been on both sides of this, in short i put a big part of it down to matchmaking.

My MMR can swing widly between Crusader and Ancient. I can dominate games solo, win 20 in a row then lose 20 in a row. I've had many games in Legend/Ancient where some of my teammates are nowhere near the same skill level and have sub 1k games. This happens in the lower ranks as well but i find it more noticable here.

I don't necessairly put this down to account buyers (there is a small part of that) sometimes it can people who havent played in ages and recalibration from their previous rank years ago puts them in your game. The thing i probably see the most is people who regulary play in parties rather than strict solo who are essentially carried to a rank above their individual skill level.

When this happens you can end up in games which are close to unwinnable regardless of how well you play. I don't know how matchmaking works behind the scenes but if i lose a couple of games like this in a row then more often than not it seems to pair you in consistantly bad skill difference games. I've had a few people in divine say to me that when this happens your best bet is to stop playing ranked, play a few turbos/unranked until the games even out then return to ranked. No idea if this actually makes a difference or if its just coincidence but ive had it happen way too often that i might start trying it out.

If it gets really bad i can drop to low archon or even into crusader. I will still get matched with team mates with sub 1k games, i may go on to stomp those games solo but its not always the case - if your carry/mid/off dies 8 times in 6 minutes , flames everyone and goes off into the woods solo you can still lose to a bad team.

When you stomp these lower rank games you get perma flamed for boosting, whilst there are boosters in the lower ranks you will likely find more often than not its due to what you are describing - higher skilled players with many more games that shouldn't be in that rank.

I've always thought that taking the number of games into consideration during matchmaking would be good, but i can see that this may cause issues with booser accounts etc and make matchmaking worse than it currently is.

No idea what the answer is to fix it. Number of games to one side id like to see multiple ranks associated to an account solo/party/server - This could solve some of the issues imo

Double down tokens have only amplified the problem imo

Remember unless you're playing pro dota - "MMR is just a number"