Engines with lack bottom end power?

Part of it is relative power.
Making stock torque levels will never really feel powerful. It feels "soft" because 2k more rpm and suddenly you're pinned in the seat.
Part of it is the ability to rev. A dyno can load an engine to a greater or lesser extent than the chassis will depending on the car weight. Making the "same" torque on the dyno isn't the same as making the "same" in the car. Engines in a car are often able to rev quicker than a typical dyno pull let's it.
A big part of how quick an engine can rev is the weight of the rotating assembly (from the balancer to the wheels), part of it does come down to cam timing.
More duration and a late closing intake will affect the amount of work the piston can do. Typically the effect is pretty negative in the low rpm range (low momentum in the air column), but the gains are substantial in the upper revs. Resonance, wave pulses, and dynamic compression are all involved. It would take a thesis paper to explain it all in depth.
At the end of the day a torque engine doesn't like to rev, and a hp motor does.