I wonder if this from the William Dietz Legion of the Damned series.
When there's no hope for the terminally ill or a condemned criminal they have one last chance to survive. And that's to join the Legion and become a cyborg. Both more and less than human, these warriors are the most elite fighting force in the Empire, they are the Legion of the Damned.
In particular the novel Andromeda's Fall published in 2012 has a number of similarities to your description:
The humanoid cyborgs were big, I seem to remember them having rocket pods attached to their shoulders and the soldiers riding on them into battle situations.
Behind them were row upon row of Trooper Is, each standing eight feet tall and packing enough firepower to grease an infantry platoon.
Shoulder-launched missiles wouldn’t be very useful in an urban environment, so all of the ’borgs carried bio bods instead
So as Chu (Chu is a T-1 cyborg) waded out into the water with his fifty at the ready and Corporal Anders riding high on his back, the resulting waves caused dozens of dead bodies to roll from side to side and undulate.
There were larger "walker" cyborgs, that were (I think) 4 legged spider tanks (heavily armed).
And all the way to the rear, towering above the rest, were the new forms commonly referred to as Quads because each had four fully articulated legs. The big walkers could function as armored personnel carriers, tanks, or antiaircraft batteries.
Seem to remember it being set in a jungle.
A section of the book is set on the jungle planet Drang.
That included two sessions of PT per day, an hour of marching, and a couple of classes. Some had to do with the Legion, but most were focused on a swampy planet named Drang. It was inhabited by a race of primitive amphibians that lived in beehive-shaped mud huts and steadfastly refused to do any of the things that a succession of interplanetary governments demanded of them. Like paying taxes and obeying Imperial laws.
I don't remember what/who they were fighting.
They are fighting the Hudatha:
For there were other spacefaring races in the galaxy, some of which would have been happy to glass Earth. The Hudathans being an excellent example. But the ridge heads aren’t going to get the chance, Ophelia thought to herself as her heels clicked on the pavers under her boots.