Playing through most of the soviet campaign so far and I have to say defensive structures in this mod are exceptionally durable. Basic infantry are effectively useless against them even if they're anti-air due to the massive damage penalty they get versus defenses and the fairly quick repair rate. Tanks are marginally effective against them, but due to their creation time and the AI's tendency to rebuild them the instant they go down it's usually better to ignore them and just rush the structures or power. The main issue however is that most of your options for dealing with defensive structures are only on very specific units (the renamed V3 Launcher) and it's a very slow way to play.
Bomb buggies... I frankly can't find a use for except clearing garrisons. They are loaded with foam against everything that doesn't seem to be a garrison structure. Even with the massive damage bonus against enemy defenses, they regularly fail to do more than a third of their HP unless they're within spitting distance of that structure, so you need a lot of them. However if you have too many together they blow each other up. Despite how big and impressive the explosion is, vehicles and infantry just yawn them off more often than not, likely due to the bomb buggy having a damage fall off and most units having far greater health than the default game. They're probably the worst unit in the game, I haven't tried demolition trucks but from what I've read on the wiki they have identical damage stats, demolition trucks are slightly more durable.
Elite units seem underwhelming, probably due to all units having more HP in general but the differences between an elite and non-elite seem very small. This might be due to the elite regeneration not being scaled up to compensate for all units having more HP. Other part of the issue is due to the elite units not getting a more generalist damaging weapon, so an elite infantry is still about as effective as a fresh from the barracks infantry against basically everything except other infantry.
Also, personally speaking, not a fan of nerfing the soviet tanks, they're supposed to be the big tank enthusiasts but now that all of the basic tanks are nearly identical (rather than being cost and maneuverability vs power and durability) they now all feel really samey and it damages the feeling of the soviets. Ditto with losing their Apocalypse tank, it just doesn't feel that good to not have a more expensive version of the basic rhino that can deal with most close-range units effectively. Not a fan of the renamed Flaktrack's massive damage penalties, as while not the greatest unit all around they at least did decent damage for their cost and speed. Now there's little reason to build them over the Borillo/Armadillo except for AA so it feels far less versatile. Flak trooper is in the same position, they really should have been renamed to "rocket trooper" as they don't fire flak guns anymore but instead rocket projectiles. Also a bit of a shame since their role now overlaps with the Tesla trooper in the anti-vehicle role rather than them being the soviet anti-infantry infantry as well as being effective against air units. Said rocket troopers are also hilariously ineffectively against enemy infantry, to the point that it can break the AI if you have enough of them firing at infantry as it takes dozens to kill individual infantry units. I really don't think that they should be that weak versus general infantry when you're dealing with explosions.
I'll need to play with the other factions to get their feel, but from what I've seen with some enemy tech, Guardian GIs are very capable units compared to the flak troopers.