The opening day peak forecasts for EC LRT were in the range of 5,500 to 7,500. Definitely below 10,000. Might be greater in the west now, with EW LRT being fully grade separated.
A failure? Definitely not. Sheppard subway had a peak of 5,500 pre-Covid. TYSSE is about same as Sheppard, or less. SSE forecast is up to 14,000 (east of Kennedy), but I think it is a bit exaggerated, 11,000 - 12,000 is more likely. And SSE is a trunk line for a huge suburb with a large population. So, 7,000 is a decent load.
The section east of Yonge will be very well used, but don't forget that it will have 3 transfer points: Yonge, Science Centre, and Kennedy. That means, riders will come and go. Unlike many existing bus routes, where the riders keep piling up until the bus reaches the ultimate destination at Yonge or at Bloor. Furthermore, a fair number of ECLRT riders will travel counter-peak, for example from Brentcliffe to Ontario Line in the AM peak. That kind of usage pattern results in a high total number of boardings, but a modest peak load.