Sealed (aka acoustic suspension) has, by defenition, poor transient response.... then again, so do bass reflex (not sure off hand which is worse, but I'm with you as regards that 'modern bass sound' in that I'm not a fan of bass reflex cabs in general, though they can be done well - see vintage Tannoy studio monitors).
The best transient response comes from open back (sacrificing bass response unless you put it in a very large baffle) and transmission lines (which require a box that is even bigger than a sealed, assuming the same drive unit). This is because the speaker is operating in a box that mimics "free air" (vs the pressurized nature of a sealed or even ported, aka strategically leaky sealed box). This minimizes the amount of force required to move the cone so it can react faster whereas sealed cabs hold the speaker back due to internal air pressure (the trade off here is that the speaker can handle a bit more power due to this added resistence to movement; it becomes harder to push the cone/voice coil to the extremes of travel).
Also, ported cabs (using the same drive unit) do not have an extended range vs sealed - the opposite is true. Ported cabs just have a response that is flatter lower, to the point of the port tuning at which the response falls off a cliff. A sealed cab will start to roll off earlier, but much more gradually providing you with lower bass frequencies, but not as much of them. This tends to sound more natural to the ear vs a ported which can be boomy or hyped in the lower midrange/upper bass (giving the impression of more low bass, without actually having more).
Further, some designers attempt to make this psychoacoustic trick even more effective (usually with smaller speakers or ones with relatively high resonant frequencies) set the port tuning so as to produce a bump in the response just before the response rolls off. I find this sort of cabinet most displeasing soundwise, but I dunno if any instrument cabs are made this way or not.
