I'd say it's a lie that Wall Street is known for short term thinking. Hell, it is even a unofficial motto of Goldman Sachs to "be long-term greedy".
Are there a large number of activist investors who want certain companies to trim fat? Yes. I wouldn't always say that trimming fat is always synonymous with short term thinking. For all the companies that are underinvesting in the future, there are 5 whose management has given them mission creep to invest in areas that incinerate capital. Especially in the current interest rate environment.
BNSF is spending money on capex because it's the smart thing to do in that industry right now. That's not a consequence of a Buffet investment. Buffet also invested in Heinz and they immediately fired thousands and are cutting costs left and right.
Wall St is known for encouraging short-term thinking.