The difference is HIMARS is modular. It can either use GMLRS rockets or ATACMS ballistic missiles.
I don't rate that distinction as relevant.
Both options the US currently use can be shot down, while the Tochka is not as capable as the Iskander and can be shot down, the Iskander seems to be rather difficult if not impossible to shoot down for the moment, which is a critical distinction.
Russia can shoot down HIMARS and ATACMS and GMLRS and everything else the US has... not all the time of course and the Orcs manage to get hits by firing at civilian targets that are not protected like military targets... which essentially makes them terror weapons... weapons to piss the enemy off.
You can also reload the unit by replacing the whole module in one go, instead of reloading the rockets in the unit one by one.
The pod loading of HIMARS is also overrated too unless those pods can be pre loaded with suitable mixes of rocket types... which they obviously can't because you don't know what you need to fire till you know what the target is and what the situation currently is.
There are dozens of different rocket types that are suitable for different targets but not just any target, so the right rocket type for the right target is important.
Just like rockets in aircraft carried rocket pods you can have a mix of rocket types and select those types for launch at specific targets... anti armour, HE Frag, submunition of various types...
Equally when operating rocket artillery you don't roll around empty and find a target and park and load a rocket pod and then fire and then load another rocket pod and fire and then keep loading and keep firing...
Once you fire there are big long smoke trails pointing to exactly where you are so you can't reload... even if it only takes 3 minutes... you have to move... and you can't reload a pod while you are moving.
When you get to a safe place... if there is such a thing then you can take all the time you need to reload and you can reload the rocket types you might want for a different target or a follow up attack.
Even with a pod you get a target you launch your rockets and then you move and the place you move to is where you reload to fire again... being able to reload in 3 minutes is no advantage and worse if you need to load specific rocket types for a specific target then you need that specific pod with those rockets in it.
Hand loading rockets is not so fast but you can load the rockets you need.
Rocket artillery remains best use for area targets rather than point targets... Smerch and Uragan and Grad and the new Tornados are machine guns. Iskander and Hermes are sniper rifles.
Plus the latest generation GMLRS rockets have more range and are guided, unlike Uragan. The original Uragan vehicle is also obsolete and out of production at this point.
In the 1980s when the M270 was new everyone ignored the fact that the Uragan was superior by many parameters to the M270 everyone was so excited about.
There is nothing particularly special about HIMARS though since there are several systems like this which predate it. One example is Brazil's ASTROS MLRS. Israel, Turkey, among other countries also have similar systems.
HIMARS is evidence that M270 was too expensive for the US and especially her HATO allies.
Performance was not amazing and the cost of introducing a Bradley BMP chassis and all that entails into their logistics just to get a rocket artillery vehicle you could easily put on a cheap truck like HIMARS shows the US MIC are greedy.
The thing is Russia has more Smerch and Tornado-S systems than Ukraine has HIMARS systems, and those Russian systems use larger 300mm rockets and can carry more of them, plus there are guided variants of these. So it is not like Russia is lacking in artillery or something. They need to continue deliveries of Tornado-S systems, develop more advanced long range rockets for it, and they can take their time developing a proper replacement for the Uragan.
If the news above about Sarma is right it seems that they are introducing the heavier of the two vehicles that carries two pod mounted launchers.
In the case of the Russian inventory that would mean it could carry a 6 tube pod of 300mm and a 15 tube pod of 220mm rockets for targets that are not so far away but need better coverage of HE fragmentation.
The Grad actually has more sensor fused top attack munitions than Smerch... Smerch has 12 rockets with 5 munitions per rocket, so 60 in total per volley out to 120km range or so, while Grad has two munitions per rocket to 30km range, but with 40 rockets it has 80 munitions...
The Grad truck is smaller lighter more mobile and cheaper so getting it 30km from an enemy staging area for armour would not be impossible... it would be way more potent than any 6 rockets from a HIMARS vehicle that likely costs rather more.
Improved range is always good, but they shouldn't fall into the same trap the US is falling in to... when the enemy bunches up for a counter offensive having tiny numbers of HIMARS vehicles scattered around the place is not as good as hundreds of Grads et al launching enormous numbers of cheap and effective rockets that are accurate enough.
Machine gun and not sniper rifle.
The Hermes and Lmur and lots of other weapons including Lancets etc can be the sniper rifle.