Are Tier 3 Melee units badly designed?
I'll start by admitting that I have only a little bit of experience playing the game. I have played 3 of the four "races" (only two in PvP skirmishes) so maybe what I'm about to say might just stem from my lack of understanding.
There are some units that are well designed for strategic engagements. The dredgecrawler from blue race, for example. It's similar to the reaver from Starcraft. It has a long range long cooldown attack that does huge AoE damage, but it's offset by its slow movement, so you pretty much have to use a vespid carrier in conjunction with it. This requires more micro, and more risk, as you lose the units if you lose the carrier. But high reward, as it has a super strong attack. High risk high reward is good strategic design.
Then you have the purifiers, which are seige tank-like units from white. They go into a stationary "siege mode" and do heavy long range single target damage, which is great for picking things off. But this is offset by its huge vulnerability in being stationary. So you have to be strategic about its positioning and engage intelligently with them. Again, high risk high reward, good strategic design.
Then you have tier 3 melee units like ice frogs and batterhorns with around 1k HP which completely crap all over the concept of the aforementioned units. And I've been seeing quite a bit of these units in skirmishes. They are low risk high reward. It will take them forever to die to dredgecrawlers and purifiers, and with how very much prevalent they are (again, judging from my limited experience) it seems like they will just shut down those units. I say they're low risk high reward because, from how long they live, it's very hard to lose them so they can get a lot of work done in the process. So instead of getting high risk high reward units to combat them (and it might even be a mistake to say "high reward" for those units when T3 melee is present) you need low risk units to combat them, such as your own high HP units. In essence, these units make the game more boring.
Now I'm not saying there's no place for giant tier 3 tank units in a strategic game. If you look at the Starcrafts, which are two of the best strategic games out there IMO, you have things like ultralisks. But they don't completely crap on reavers or siege tanks. (They do shut down siege tanks pretty hard if you use dark swarm, but that's another hard to execute spell from the defiler, a high risk high reward unit.) And their HP isn't tuned so bloody high that they can ignore hits from things like reavers or tanks; a group of ultras a-moving into a fortified position with reavers will still get absolutely destroyed. (Again, this is good design; punishing a player for doing something as mindless as a-moving an army.)
So I wonder, does the currently tuned version of tier 3 melee units shut down a lot of fun and hard to execute strategic options? So far, for myself, I feel discouraged from playing the high risk high reward strats and I feel like I need to gravitate towards the easier, low risk boring options to have a good chance. But I'd love some input from players with more experience than me, maybe I'm completely wrong.
You are not completely wrong, but there have been patches of this game only a month or so back when maxed our ranged dps armies would just focus fire down these big melee units very fast and it didn't seem like they were out of line at all. As you say, ultralisks are capable of existing in SC2, likewise big melee could work in Atlas. One solution is to slow down tech, so that other kind of armies are more well upgraded and higher population cap when the big melee units hit the field.
In sum though, I think this is an awesome post on a topic that needs to be discussed. At the moment though, I'd ask for a little patience to see how the new patch affects the prevalence of big melee, before we jump to conclusions.