As mentioned earlier by @glauber You have to look at the content you get proportionately.

Looking at the base game that came out about 22 years ago, I don’t know what the price was. So the base game you’re referring to is a graphical overhaul of an existing old game, in that sense the price was reasonable but it’s a poor comparison. Compared to the last DLC which contains 2 civs, this downloadable content offers more value. In addition, the developer has added new features that were not technically successful in this game before, which gives the player unique new gaming experiences, so it is not just a doll with a different skin.

Let’s say the base game has also received a change with a new unique unit, so you can get it for free as the owner. Indians were changed to Hindustans with the following (free) changes and additions:
unique units

• Ghulam – A unique Hindustani infantry unit that propels its spear across multiple targets. strong vs. shooters. Weak versus cavalry.
• Imperial Camel Rider (Camel Rider)

Unique buildings:

• Caravanserai – economy building. Handles and increases the speed of trade carts in a radius of 10 pieces. A unique Hindustani building.

Unique Technologies

• Grand Trunk Road (all gold income 10% faster)
• Chatani (hand cannon + 2 sets)

Team Reward:

• Camel units and light cavalry + 2 attack against. buildings

In my opinion, your judgment isn’t really fair regarding this DLC, but you can always wait until there are discounts on Steam, for example, as it is now for older DLC.