<rant>
Starship Troopers is pretty infamous for the extent to which the director hated the source material, and the movie is intended to be a parody - slash - condemnation of the book. It is extremely clear that nobody involved with the production cared about the actual points the book was trying to make, and as far as I’m concerned it’s dubious as to whether anyone actually read the damned thing.
</rant>
That said, you are quite correct that the soldiers in the movie represent the height of idiocy. There is no evidence of armor or artillery support, and IIRC only one scene that demonstrates air support. Modern military strategy hinges on the idea of combined arms (that is, multiple weapon systems acting in concert). It is often easier to defend against a single type of attack, so modern soldiers try to place every type of weapon (infantry, armor, arty, CAS, etc) on the target at the same time.
It’s not clear in the movie that they are exercising any tactics at all. I got no sense that they knew what squad or platoon they were supposed to be in, or what each unit’s sector was supposed to be. They just all kind of ran around in a disorganized mob. Perhaps the filmmakers were so critical of the book’s conservativism that they wanted to make it look like Soviet Russia, or perhaps they were just a bunch of fucking idiots who didn’t care.
FWIW, the book doesn’t really emphasize the war part of it. The point of the book is the examination of how their military (and more generally, their society) functions. I haven’t done an exact page count, but I’d be willing to be the book devotes more time to Rico’s stint at officer candidate school than the actual battle scenes. In what battle scenes we do see, each Mobile Infantryman is heavily armored, can make rocket-assisted jumps, and carries area denial and tactical nuclear weapons. In the very first chapter Rico nukes a piece of enemy infrastructure basically for giggles. The infantry in the book are far better equipped to handle this type of combat than their movie counterparts.
I’ll offer one more point, which is kind of a criticism of the entire “Space Marine” genre as a whole: I cannot conceive of any reason to land human troops on the surface of a deserted planet. It’s a trope that we see over and over in fiction, whether it’s the novel “Armor,” “The Forever War,” “Warhammer 40,000,” or even “Star Wars.” In real life, we don’t go around glassing entire countries because (A) contrary to what the HRC crowd might think, humanitarian concerns do play a role in our decision-making and (B) nuclear warfare is not cool.
If the planet is full of xenocidal semi-sentient insects, with no infrastructure or other objective worth preserving, these moral constraints go out the window. I’d just nuke the shit out of it from orbit and move on. The only time soldiers should even set foot on the planet is if there is some resource or infrastructure that needs to be captured (such as a brain bug). The movie was filmed in the goddamned Badlands, after all. What strategic territory were they trying to sieze? Once you establish air/space superiority and isolate the critters on the planet, you can just “island hop” to a more strategically important area.