I highly doubt the average buying price was anywhere near 60 which is a big factor. 

Well, that sucks. I really don't like Bethesda, so I decided a decade ago to never buy anything that had their name on it, even if they weren't the dev. I got Dishonored as a PS+ game, and played it last summer. Loved it. So much, I plat'd it and bought 2 of the 3 DLCs. Shortly after, I bought Dishonored 2, and plan to but it's DLC as well. It brought me around on at least buying games Bethesda merely publishes.

Arkane were good devs from the get go - Arx Fatalis is quite loved in CRPG community and Dark Messiah of Might and Magic was really fun game. I don't think that Bethesda put many creative constrains when they acquired them, though I personally don't find any of titles under Bethesda to be as good as when they were independent.

Yeah, I don't believe Prey sold well at all. But in regards to Prey's lackluster sales - Bethesda is solely to blame for that as it had next to no advertising and very little hype build up. When ever it appeared at gaming conventions, it was always put on the back burner it terms of product awareness...

What bizarre budget did they have to the point that 2.5m sales is considered bad?

Well, back when Tomb Raider launched in 2013 and sold 3 Million copies - Square Enix made a statement saying that it underperformed in sales. Video games are more expensive than people think. The average cost of a video game is $25 Million, and that's not including advertising. Landmark AAA games like Grand Theft Auto and Fallout, for example, cost upwards of $100 Million... 

Probably had a pretty typical budget for that kind of game.

It's not Fallout or Elder scrolls sized sales that's the problem Just stick to RPG's Bethesda, might as well get rid of Doom and Wolfenstein and hide Rage under the bed.

That's too bad. I have heard nothing but good things about this franchise.

I don't think it so much about budget more to do with expectation of growth you see it all the time in business where a company makes a healthy return on investment but it's stock drops because of higher  expectations, I remember Square-Enix talking about a disappointing Tomb Raider even though it had sold if my memory is correct  around 5m in its first 3 months, because they had set their sales expectation to over 6m even though previous Tomb Raider games averaged around 2-3m level . 

Still they will look at the budget and say can we invest this time and money somewhere else for a better return and you can't really blame them with a game that sold less.

About the game itself the first one I enjoyed to a point the point being for a game that supposedly gave you choice it pushed you toward  the stealth option by punishing you if you mixed it up.So that put me off playing dishonoured 2