RPG is an upgrade. Bazooka doesn't require any techs.
Other anti-tank and energy generating options are also available later in the tech tree, though probably too late..?
(Though what about planes in main anti-tank role ?)
Compared to solar power, serpentinization is expensive and inefficient, volcanic power is expensive and needs a volcano, nuclear power is expensive, late-game and need a source of radioactives, by the time you get any of them you have probably already had to delay your economic development for lack of energy, and you're not any more guaranteed to roll any of them than you are solar power. Fuel power plants are okay, but require a significant up-front investment in metal to build and fuel production (which costs even more metal to set up) to run, which may force delaying other early development.
After seeing how badly my RPG troops struggled against early light tanks in a recent multiplayer game with a tech 4 start (so RPG and Padded Envirosuits tech were already researched), I have very little faith in the basic zookas being a viable defense against light tanks with even 50mm armor. Maybe if entrenched in dense forest. Foot troops seem to need at least 3 or 4 levels of RPG or armor tech to hold their ground against even basic tanks, unless defending favorable terrain. Otherwise the best they can do is slow them down (with increasingly catastrophic losses the less armor & RPG tech you managed to roll).
That is why I advocated for High Velocity Guns as a critical tech rather than RPGs - anti-tank guns aren't great either since they're many times more expensive, but they should at least have enough firepower to fight tanks effectively if hidden behind meatshields. Arguably, tanks are the most efficient counter to tanks, but you're going to have to roll High Velocity Guns anyway to rely on them for that in the midgame. Strike aircraft could be total garbage depending on the gravity and air pressure, so they're not a reliable countermeasure.