Am I missing something

So I follow roadkill an hot rod garage. I just watched the last episode upgrading there fury station wagons brakes an top end of a 500cu something or rather stroker. An they were hoping to make 500 hp with this. After having this thing tuned on a dyno they got it in the low 400 ish power range. An they had some nice parts put on this thing. So my thoughts were if these guys who do this for a living an have what ever they need to build these engines, an barely clear 400 hp with this big stroker motor.( Not that 400 hp is anything to sneeze at)
How is it a lot of post I've read say something like 400 horses is easy to get with a 360? I guess I'm confused. Not trying to poke any bears I guess I'm not understanding how a stroker engine of that size an with those kinda parts isn't making a lot more ponies. Anyone else watch these?