EDIT 10/11: Editing with additional thoughts now that I've had a bit more time to process the changes and we have info on the missing passives.
Here are my thoughts on Merc dps changes as a long-time merc main:
What is a merc?
To me, when I think of the merc class, I think of a fairly tanky class with reliable ranged damage that doesn't necessarily bring a whole lot of group utility to the table, but brings a lot of individual utility and is able to keep themselves alive when the going gets tough.
Thinking outside of swtor and more generally to the star wars universe, a merc is a bounty hunter with all the right tools - able to compete with stronger, force-using opponents like jedi and sith through a combination of sheer willpower and preparation. Whatever gets thrown in their face, mercs have a trick up their sleeve to throw it right back.
Unfortunately, merc as it exists in swtor doesn't quite live up to that - its damage (particularly arsenal) is far too weak and its abilities are not very unique or flashy - they mostly just boil down to a different way of shooting someone. These changes do not seem to go very far in pushing merc towards the right direction. Mainly, these changes are a nerf to merc defensive cooldowns, which, although in-line with the general philosophy of 7.0, hurts merc's only real strong suit without bringing any additional utility to the table. Without more adjustment, I see mercs continuing to be left behind in the 7.0 era.
General Stuff
Thermal Sensor Override and Vent heat have been merged. I am not sure how to feel about this yet. Given that TSO on live should always be used with blazing bolts/unload for maximum heat-venting, it seems like this will restrict when to use vent heat as well. It could be a good change once I've adjusted, but for now I am a bit concerned it takes away options for heat management and adds more reliance on a single "oh sh*t" button.
I'm still not at all sold on the idea of making threat drops a choice. Tanks will hate this. Despite subpar sustained damage, nothing pulls threat like a good arsenal merc. I would prefer if the threat drop were a given ability and the defensive bonus attached to it was separated to be the choice instead.
Explosive dart and missile blast are still here. Why, exactly? When I heard 7.0 was adopting a streamlining philosophy, these were the first two abilities I thought of that could easily be removed and it would have little to no impact on how merc plays. Yes, I know explosive dart can dot spread for IO, but so can fusion missile. And yes, I know IO has the missile blast proc and the root utility exists, but generally it seems like even sub-30% it is better for IO mercs to gain supercharge stacks unless the boss is going to die immediately. And the root, while maybe useful in pvp, has a big tradeoff with other passives and could easily be folded into other merc abilities. Without major rebalancing, these abilities only function is to confuse new players who don't understand they shouldn't be part of the rotation.
Finally, choosing between reflect, hard stun, and hydraulics is gonna be a tough one. I would really rather rocket out become the choice here. Hydraulics, although only a minimal speed boost, is significantly easier to use and provides great raid utility from its ability to negate knockbacks.
Arsenal:
The spec looks and feels mostly the same from what I've seen. I'd say that's a good thing, but I was honestly hoping arsenal would get something a little flashier. As an arsenal main since launch, I love the class but even I can't deny people are right when they say it's incredibly straightforward (another way to say boring). It also had to suffer the 6.0 era as the lowest parsing dps class. In the era where the Mandalorian TV show helped reinvigorate star wars and created a new generation of bounty hunter fans, it's criminal that arsenal is this boring and underpowered. We have a couple types of missiles, and a couple ways to shoot people. What about those whistling birds from the show? Anything to give the feel of a professional hunter equipped with all the tools to take on epic enemies (isn't that what "arsenal" means?).
Along those lines, I really hope the primed ignition tactical will make a return, or (even better), the priming shot DoT will be added as a passive. This was a great addition and added a good deal of strategy in terms of getting the most DoT ticks to an otherwise incredibly simple rotation. Arsenal on live is entirely built around maximizing your damage from this DoT - please, please make it a built-in part of the spec, or replace it with something just as interesting. This pts arsenal rotation just feels blah.
IO
IO also looks and feels mostly similar to live. Seems like jet boost no longer gains 2 supercharge stacks (or the passive for that is not there yet?). I am cool with this change if intended - it was pretty weird that there ever was a class with a rotational knockback. Honestly, thermal detonator should just replace explosive dart as well (if that ability has to still exist - which it shouldn't unless it's damage value is significantly increased from live). Not much else to comment on here.