You... simply cannot take the numbers from one war and blindly apply them to a totally different one. The comparison isn't apt for a number of reasons.

First, Russians are generally on the offensive, which means pushing into Ukrainian controlled territory.

Often, they are pushing into defensive lines that have had years of fortification.

Second, there are a lot more Russians in Ukraine. To kill 125k people, you have to find 125k people. It's a lot easier to find a Russian in Ukraine that it will be to find an IRGC soldier in Iran if there's an invasion and guerilla operations in response.

In Iraq after the conventional military phase, the US killed ~26k insurgents over the course of a decade (and also captured ~120k).

Iran is bigger than Iraq, has far more people than Iraq, and has much bigger logistical burdens for an invasion.

I could believe that the US Military is quite capable of running some small scale targeted operations within Iran successfully. We can probably pull off operations to do things like attempt to seize and secure uranium stockpiles if we know where they are (though such an operation could also go catastrophically badly, too).

I think the US Military could invade Iran and topple the regime, but it would be an enormous lift, and I think there's almost no chance we would have the political will to sustain the costs and casualties that a total invasion would entail.

thats in a scenario with soldiers pushing into no mans land under permanent drone control. Israel demonstrates much lower stats when enemy hides underground. I would imagine having no boots on the ground will lower the numbers further.