There’s no “larger glider”. The name “glider” refers to a single specific pattern of five cells.
"Some patterns require a very large number (sometimes hundreds) of glider collisions"
At that time Andrew Wade had already created the self-constructing Gemini spaceship, which needed 173449 gliders to build ( https://conwaylife.com/wiki/Glider_synthesis#Spaceship_synth... ). The recipe could have been reworked to be a little cheaper, but nobody bothered at the time -- and now it can be done in fifteen gliders instead.
If you want to see the construction happening, I'd definitely recommend the old Gemini recipe over an RCT-based one, though! RCT cuts down the cost in gliders to a minimum, but at a terrible cost in the time you have to wait around to see the completed object.
Gliders are generally considered to be the "lowest common denominator", though, so adding complexity by allowing more types of spaceships isn't usually seen as an improvement.
... It also becomes possible to cheat: I suspect we could put together something like an "RCT8" if we allowed Corderships as well as gliders in the list of allowed moving objects that we start with. (2-engine Corderships' "engines" are switch engines, and we have to build four switch engines to get the RCT reaction started. Could probably just shoot down the extra switch engine with one glider, and go from there.)