i think they are pretty janky but will beat up the average field at a store championship.
there are a lot of factors going on but here are few.
there is no magnum opus in the field. infinite money on the runner side is a problem for pure flatline decks. they cannot flatline if they never have more money than the runner and usually cannot reverse course and start chaining out agendas because they cut corners on ice.
anarchs have the best tools to empty the kill cards and transaction econ out of the corps hand but are currently considered the weakest runner faction.
the pure flatline deck is only one type of weyland deck that someone may bring to a tourney. even if you are a good player and know to stay ahead or even on money how quickly can you identify the type of weyland deck you are playing against ? some weyland decks rush agendas. some are hybrids that score agendas with a back up scorch plan etc if you misidentify your opponents strategy you may be in trouble.
its also hard to dial back the aggression in a field with HB and NBN FA also present. say round 1 and 2 are against NBN rush and HB FA. are you disciplined enough to dial back on the aggression that won you the first two rounds when you see the weyland id card? maybe. maybe not. it takes a lot of discipline and experience to change gears rapidly.