There is 0 gain for riot to do this. Note that even a modified ELO system (whats used by matchmaker) Requires several hundred games to properly place some one with high accuracy of their assigned skill to their true skill.
If you believe this is done to make players play more games, the system already requires a high number of games for accuracy, extra step accomplishes nothing.
If its to make money, There's no profit in pissing off players to the point they quit and any in game transactions that influence gameplay that can be purchased with RP, can be purchased with BE. Extra step accomplishes nothing.
If you think you get punished for a win streak. No reason to do this as there's no positive end result by forcing 50% win rates. The system will try to learn your strength and skill then place you on paper with other players it thinks are at your level. Takeing extra time to search for bad players would increase que times, if riot was willing to blatantly up que times they could instead do it with systems that hunted for positive players, folks with similar # of ranked games played, etc.
this Forced losses BS comes up in team games and mobas all the time because people hear "our match maker wants to give you 50% chance for a win" and they think its forced or riggs it. Google Dota 2, Overwatch, Smite, Heros of the Storm, you will find threads complaining about 50% forced win rates. Go back to season 1 and 2 in league and hey you can find complaints about Forced win rates. its rubbish to claim its forced when it can accomplish the exact same end goal by just working as intended, when some one says YES ITS TO MAKE PEOPLE PLAY MORE GAMES, well its a law of large numbers system that already expects and wants you to play more games the hell do you need to add extra work to accomplish the same end goal. Honestly why would any one bother with that?
Your talon was b5 and his MMR has tanked because he is a bad talon. His main is lux with 200+ games and 52% His talon is under 50 games and a terrible 29% win rate. Theres no way for the system to reliably know who he will play, so theres no way for it to try to dick you in advanced reliably.
By all means, Give me a logical reason that riot would want to rig their game and tilt their players.
Alternatively, if you want a legitimate complaint, Duo Queing is likely the reason that talon ever ended up on your team. Enemy had a b5 nid duoing with a silver. it factors both of them then adds a bit of extra MMR to their team strength in calculation.