[tempnow987]

The better comparison is probably Falcon 9 and Crew Dragon in terms of mass / mission etc. Starship is in a totally different class

For Falcon 9 - it will look slower on takeoff as well. One reason not mentioned yet is that after engine start, Falcon is held down until all vehicle systems are verified as functioning normally before release for liftoff. So they can do pressure / thrust etc checks on the ground before releasing.

With solid rocket motors especially - once you light those you are pretty committed.

[ericbarrett]

Mass does not strictly matter, it is the ground TWR of the launch config. Heavier rockets do tend to have a lower TWR but it is not a universal rule.

Starliner is also held for confirmation of all systems being functional even with the SRBs. Better to let them burn out on the pad and clean up the mess than to risk release with, say, asymmetrical thrust. That said I'm sure there are variances between the two rockets' procedures which could make one appear faster.

[tempnow987]

Interesting that they hold with SRB's lit.

I think SLS does 90% thrust on main engines - then lights SRB's but SRB ignition is takeoff. A problem at that point is launch escape abort (capsule to safety) if for example one SRB lit but the other didn't for some reason. Not sure it can otherwise manage the asymmetric thrust.