Depends how you like to define bandwidth.
Small signal bandwidth as -3dB from flat-top, is not
a very useful descriptor of a T/H amp's performance
when what you care about is a settled-to-N-bits
time window. And T/H amp intra-cycle performance
is neither continuous-time nor small signal - it's
clocked, discontinuous and dealing with switch charge
injection on top of natural amplifier settling.
I'm no ADC specialist but you need way more BW
to get decent THA - ADC lineup performance than
your sampling clock frequency. Off the cuff I'd call
it fClk*2^N or something like that - figuring T/H amp
is a capacitor burdened unity gain follower, and you
want about 1/2^N gain error @ freq.