Why recommend RED for client-side routers? Better to use more modern AQM approaches such as fq_codel or its successor cake [1][2]. Both of them are far easier to apply to client-side routers without fussing too much with settings: setting your download/upload bandwidth limits is enough to get nearly all of the benefits.
Other than that, you're 100% correct on Spectrum's ridiculously high buffer sizes on their end.