Brighthouse is known to throttle, so this could be part of the reason. Most likely the reason is because of speeds. FiOS is wayyyy better quality than Brighthouse. When I had Brighthouse I was promised 10Mbps, and never got the full 10. Verizon beings the fiber optic cable straight to your house. Bright house uses fiber optic up as far as the neighborhood/community area(sometimes further) and from there they use copper wire to people's homes. Copper is much cheaper and this was what was used mainly. It costs Verizon a lot of money to being the fiber optic cable to your house.
With Verizon, I was promised 15Mbps and got 22-24Mbps regularly. I upgraded recently to 50Mbps and have gotten 56-58Mbps plenty of times. There was even an article that came out that shows FiOS is known for having faster speeds than promised. Brighthouse says that you can get up to those speeds, but it might not happen often, if at all.
That being said, I would switch to Google Fiber in a heartbeat. I wish it would come to Tampa.
Yeah I fully agree with what you're saying. I'm an electrical engineer and computer nerd. I've had FiOS for about 7 years now and have the 50/25 service. What I was referring to though is on a FiOS connection for both scenarios, I logged in with a Brighthouse login and then later with a FiOS login. The stream quality using the FiOS login was better than it was with the BH login. So what I'm saying is that maybe ESPN actually throttles their stream from their servers based on who your ISP is. Maybe the ISPs delegate to ESPN on what bandwidth to allow their customers to use.