In fact, to the best of my knowledge, the SM-6 missile is capable of intercepting MRBMs, whereas the HQ-9B has limited capability against SRBMs. I am unaware of how effective the HHQ-9B would be against sea-skimming targets.
We don't really know how their respective capabilities compare in terms of their ability to engage ballistic missiles. For example, while SM-6 is of course is a capable missile, it isn't an exoatmospheric interceptor and defends against MRBMs in the terminal phase.
Against ballistic missiles in the terminal phase, between SRBM and MRBM things really just lie on a spectrum of where one draws the line between classes (and sometimes they bleed into each other).
For example, the export version of HQ-9B describes defending against TBMs with a range class of 1000km, which is also within the MRBM range bracket, and it wouldn't be a surprise if the domestic version of HQ-9B outperforms that, and we know they're introducing upgrades to HQ-9B.
More importantly, both HQ-9B and SM-6 would be intercepting ballistic missiles in the terminal phase anyhow.
Furthermore, the effectiveness of the HQ-9/9B against low-altitude supersonic missiles falls short of expectations. It did not perform as expected during the India-Pakistan conflict on May 7th against brahmos and LO scalp missiles.
Not so simple.
We don't know how many HQ-9 or HQ-9B units Pakistan had, or how many missiles were launched, how many targets were intercepted, and how many targets were missed, and the relative ranges and trajectories of interceptor missiles and targets.
There is also the factor that Pakistan has limited strategic depth and it is likely their HQ-9 units would not have had networked AEW&C support.
Ultimately, no matter how advanced one's ground based air defenses are, their radars ultimately are still on the ground and bound by radar horizon, and if an opponent is sensible and uses weapons in a low altitude ingress flight profile, then you aren't going to be able to defend against them if you don't have either:
-Plentiful strategic depth with forward placed radar pickets to develop an organized radar pictures forewarning, and/or
-Ideally AEW&C networked with your IADS to provide long range radar horizon surveillance.
The dynamics and disposition of ground based IADS and naval IADS are also not always similar.
- GB IADS have to contend with often being situated some distance away from one's high value assets that they are defending (as their role is also to cover large swathes of national airspace!), meaning they may not always be positioned "optimally" to engage an enemy's attack because they have to cover multiple approaches and also cover a larger area for general airspace defense purposes, which allows a competent attacker to try and plot weapons in a way that has the lowest risk of successful interception by GB IADS (e.g.: skirting at the edges of their effective ranges). GB IADS also have to deal with ground based structural interference (buildings, valleys, mountains, even trees) which affects radar horizon for your ground based radar but also may create blindspots.
- Naval IADS on the other hand, may have their platforms (i.e.: AAW ships) deployed specifically to defend a localized area in support of a high value asset like a carrier (for example), and there may well be a higher chance that the weapons the enemy will fire against your high value asset thus will be also going in the general direction of your AAW screen. The nature of the ocean of course is also that there is virtually no surface structural interference and virtually no blindspots (except for other ships nearby), meaning your AAW ship's radars can be expected to probably see out to their own effective maximum theoretical radar horizon much more easily than GB IADS.
For the purposes of HQ-9B in terms of its performance as a weapons system, there is nothing particularly useful that can be learned from its performance in the 2025 conflict, because we have next to no useful information.
All of which is to say, essentially you should disregard the prior points of your post that I've quoted above, and just dismiss them as misinformed opinions and replace them with "we don't know".
So, I wanted to know: is the HQ-26/29 system much like the SM-6—capable of simultaneously intercepting aircraft, high-speed low-altitude missiles, and short-to-medium-range ballistic targets?
HQ-9B is the PLA equivalent to SM-6, with similar roles for LR air defense, defense against low altitude targets (including sea skimmers), and terminal defense against ballistic missiles.
HQ-26 is a weapon whose identity we have yet to confirm.
HQ-29 is the GBI equivalent for ICBM esque class targets.
