Your Nation is a Confederacy
The national force comprises almost purely helicopter borne elite infantry because such troops require a higher degree of expenditure and training. The individual states/territories that make up the nation as a whole field mostly infantry and artillery units. Armored warfare isn't a high priority for geo/political reasons.
This layout somewhat reflects the CSA/USA forces in the American Civil War, and USA forces in general before WWI. Essentially each state produces/maintains "baseline" forces, with the national government maintaining a core of professionals and specialist units beyond the scope of individual states to equip. In your case, helicopters and heliborne infantry become the purview of the Nation due the expenses involved, but also because of the inherent disadvantages of those units. It means that the National Government could not easily use its troops to combat state forces. So the national government, either by law or historical consent, does not field any land forces besides helicopter units. Sort of like how the UK has a "royal" navy and air force, but not a royal army.
Meanwhile the states would be fielding soldiers specific to their general needs. So the desert-facing state might decide to field armored cavalry units and long-range artillery, whereas the mountain-facing state would invest in static defenses and garrison troops. A state bordering Indonesia might disregard land-based forces entirely and concentrate on marines and swiftboat-style navy vessels. None of the states bothers much with armored warfare because tanks are either not super useful/cost effective (mountains, Indonesia) or flat-out too expensive (desert). Plus for the desert state the National Helicopter divisions can more easily do the job required against insurgents/bandits. In times of national emergency state forces are amalgamated into the national army, but are still somewhat distinct. (In the CSA for example, state troops in the "national" Army of Northern Virginia could still be recalled/have their operating area restricted by their individual state governments.)
Your helicopter national forces would be excellent support/rapid assault troops in all three environments. But if they were 100% of the armed force they'd have huge problems everywhere apart from (maybe) the desert. Both mountains and forest/jungle can create severe limitations to helicopters/air assault troops. In Vietnam for example there were still many more divisions of non-airborne/air assault units. Meanwhile in the various dustups/wars between India and China, and US/Soviet operations in Afghanistan, you can see the restrictions of helicopter operations in mountains.