Yes, when so many popular and similar brands are owned by the same company, then that company very likely has too much power. Most people don't realize that Tinder, Match.com, PlentyOfFish and OKCupid are essentially one and the same. I don't know about splitting up the company, but at least it should be more transparent.
I think that all of these separate companies being owned by the same company gives that one company far too much power. For a single company to have so much influence over multiple companies in the same sphere is troubling, especially when each of these companies is selling a drastically different message.
The fact that one company owns several of the largest dating sites is not too much power for one company. Each brand that this company has represents a different demographic of user, and they are maximizing their profit in a smart way by utilizing these different brands. Someone that uses Match.com will likely have a different intention than someone using Tinder, so it is important to have a variety of brands in order to reach the widest audience.
It is my belief that one company owning several dating website should not be a concern to consumers. There are innumerable ways to find dating partners using the internet, such as social media, mobile applications and networking sites. I think it would be a stretch to call one company a sort of monopoly in the relatively minor industry of online dating.