Sombra’s movement, I’d argue, isn’t really the part about her that you play her for. After all, her movement isn’t good because it’s fast, it’s because she’s invisible. The boost she gets helps her get around, but because invisibility forces her to be inactive, that speed isn’t that great in practice. It’s just for the sake of positioning, and doesn’t have impact in and of itself, other than perhaps a few particularly lucky getaways, in scenarios where Translocator wasn’t up for whatever reason.
What I see these changes as are ways to increase what Sombra should be doing, which isn’t sprinting to positions, but remaining hidden and discretely getting into those positions ideal to her. Without being pressured by her own timers, Sombra can more comfortably be in the opportunities that she wants.
And that doesn’t require a raw buff. Yes it would objectively increase her pickrates if she got raw buffs, yes it would objectively make her a better hero than her current position, but that isn’t healthy for the rest of the game. It would not be healthy if Sombra only got buffs here; she can be invisible infinitely, she can Translocate infinitely and with security that her Translocator isn’t compromised, she can contest points, and she still has that amazing speed while invisible. The goal of balance changes isn’t to make weak heroes stronger or vice-versa, it’s to balance the hero, and that’s almost always going to mean taking some stuff away in favor of stuff that’s much more important. Raw buffs don’t tend to do well with the game unless it’s something genuinely minor, or if it’s a change meant to go hand-in-hand with previous changes.
Also, we do have some Blizzard comments that direct us to what their goal is for Sombra through these changes. In the June 28th patch for PTR, for Sombra’s dev comments we had, “These changes allow Sombra to more easily play as an infiltrator and scout for her team, as well as give her time to pick and choose when to reveal herself to ambush her enemies.” We also have this post from Geoff, where he says, “These changes are really interesting for her as now she is in complete control over when she reveals herself, allow her to time her hacks better for her team, or go for a back line ambush during a critical moment in a team fight.” Then there’s this other post by Geoff, which sounds a little familiar: “The goal of these changes is to make her stronger overall, even if it means being slightly weaker in some areas.”
So from here it seems fairly clear what their intention is. They want Sombra to ambush and get those surprise hacks while navigating the battle field with less detection, but in doing so, they have to clean up the areas where this wouldn’t feel fair, namely in how she could contest objectives or move incredibly fast for an extreme amount of time while also being unseen. Admittedly, I’d still love for some more comments from the dev team to get an idea of what they’re thinking, but game devs usually have their hands-tied on these matters for a number of reasons (namely that their userbase is unstable and sometimes more information is just more fuel for the fire).