It does seem as though Towers has possibly the weakest ride availability of any of the Merlin parks at the moment.
I was at Legoland and Thorpe Park on Sunday and Monday, respectively, and neither of those parks seemed to particularly suffer. Availability and uptime was pretty good at Legoland, with nothing closed all day to my knowledge and breakdowns kept to a minimum, and at Thorpe, the only thing closed all day aside from Hyperia was Detonator and aside from one or two small stoppages, the number of breakdowns seemed to be kept to a reasonable minimum.
With Thorpe in particular, people have often moaned about how poor their operations and ride availability are, but I would personally argue that on my recent visits to both, Thorpe has had better overall uptime and ride availability than Towers.