Well, like I said, this is a tech you get after at least you’ve taken some damage, not right at the start of castle age. You’ve got more than enough time to get a castle later on down the line, the elephants just help to justify that decision.
That returns to my earlier point about retroactive bonuses.
Tusk Swords, for example, is largely beneficial based on the strength of your current units. IE, if you have 10 units with half hp each, then getting tusk swords is only going to give you half the value. Especially since your enemy likely already has counter units out.
But Medical Corps is different. It actually works best if you have a weakened army, and it applies to a variety of different unit types, allowing greater latitude in your progression forwards. Where a Khmer player finds themselves somewhat obligated to use more battle elephants, a Dravidian player can freely opt into Armored Elephants or Elephant Archers as needed. Unlike the Khmer player who likely already has counters out, the Dravidian player can swap into something that they haven’t yet countered.
The only thing it doesn’t really help against is monks, which counters most elephant units roughly equally, but that’s why +5 LOS and all.
Plus,in my experience Dravidians almost always end up getting pushed back in mid castle age, so they’re going to want a relatively early castle anyway.
Like I said, this is just to demonstrate relative power, not to simulate a practical situation. That’s why it’s actually biased in favor of the knights in terms of resources; it’s just to display relative potency of different techs. In terms of value added, Medical Corps offers approximately equal value per cost to Iron Casting, without even taking into account the long-term value. That’s pretty good for half of a tech!
Cavalry will always have an agility advantage, but that doesn’t mean you go without upgrades!