Then the battle itself drops a stupid amount of pickups throughout, so I was actually at full health a little bit after starting the battle. Every attack either has a huge tell and/or wind up time in this phase (flashes red before the charge attack, opens mouth and roars before the beam attack, missiles take a very long time to reach you), meaning it's fairly easy to maintain most health. You can finish this phase of the battle with full health pretty easily (although if you misread one of the more aggressive charge attacks in the third phase, and no pickups are dropped after that, I can see you ending this with a couple tanks lost).
Which brings us to the second phase, which, admittedly, is slightly more chaotic. The ground slam doesn't have as long a tell as the attacks in the first phase (although it is still fairly easily avoidable and totally ignorable if you stand on the discarded husk from the first phase). Visor switching is annoying, but other than the annoyance of having to frantically do it in the middle of a temporary opening to attack, it's not too bad. The Metroids can be a pain in the ass, but using the power bombs instantly clears them out (and at least one of them always drops a power bomb pickup, while the other drops health, so you can keep this going pretty much endlessly every time the Metroids are spawned).
Now I will say the attacks in this phase are more aggressive, more chaotic, and there is a lot more to keep track of. In this phase, yes, it is much easier to lose health (though, again, almost every attack is easy to avoid, and the game provides frequent pickups as well); however, that makes it moderately challenging; it's more like the Thardus battle, which is more a battle of attrition and chip damage while trying to keep your health up and outlast it, than it is a challenge in the sense of requiring constant top notch response and input from the player at risk of heavy damage if you fail.