Once you include getting out of Stockholm to the airport, security, boarding, the flight itself, possible baggage collection, and the trip into Umeå, I would be surprised if the total were much below 4 hours. Comparable German domestic flights such as Hamburg–Munich usually took me around 4–4.5 hours in practice in the past when traveling for work before the pandemic.
That makes the train a 6–8 hour alternative to a roughly 4-hour flight journey. Whether that is viable depends on the traveller, but it is certainly more competitive than “1 hour versus 8 hours” suggests.
I admit that for me, living about an hour north of the Hamburg main station but only 15 minutes from the airport, the plance for a business trip in Munich can still be a viable (albeit seldom taken) option. More often than not, if time permits, I take the train, work on the train. But as said - there still are situations, that make flying such a distance viable (to me).
I just wanted to point out, that it is not as clear cut as 1 hour vs. 6 to 8 hours.
Of course there are a lot of variables, if instead I leave from my house the aircraft would actually be faster, mostly due to the extra time it takes to get to Central London and from Waterloo to Euston.
In reality we usually drive in about 6-8 hours because, as a family of 4 traveling, it's considerably cheaper even before you take into account having transport on the other end.
I and a friend once started at Stockholm Central station to Malmö Central Station at the same time. I boarded a bullet train; he took the bus to the airport ... We arrived at the same time six hours later.
I've been looking at travel in Japan recently. Between Hiroshima and Tokyo, the bullet train (fast Shinkansen) and flight are both about four hours.
A bullet train is much more comfortable than flight within these limits because there are so fewer steps: no travel to/from airport, fewer tickets to book and often no check-in or security checkpoint.