Disclaimer: Never played Star Realms, but I assume it is very similar to Hero Realms.

And no, it’s not similar at all. There is a lot of stuff added on top in Undaunted that makes it not a deck builder in the primary sense. You move your troops around on the battlefield; positioning, cover and distance are as impactful as the stats on the troops cards. Also there are only a handful of different card types - scout, gunner, machine gunner, sniper and mortar. All cards of a type are technically identical.

You could think of the deck as both your “health bar” and your available options per round.

Each troop token on the battlefield is represented by several cards in your deck (the soldiers that compose that troop). If your enemy hits, you discard one of those cards from the unit they hit. If you can’t do that any longer, you remove the token from the battlefield.

Also the cards dictate the options you can do per turn, such as move, fire, taking cover etc. That means if you don’t pull the “bravo scout” card, you can’t use the bravo scout token this round.

Summarizing: Undaunted is a great - snappy, easy, elegant, but also deep - “dudes on a map” game. But if you expect “only” a deck builder, you would have the wrong picture.