the spam from a roamer is very valuable for the area denial but its not that big of a deal who does it. alot of times its easier for a roamer to since he is the one who sacs so you dont have to send someone back to spawn and risk a 4v6 uber fight if he doesnt do anything with his sack. but on viaduct roamer is the best option since scout is so insane on that map.
edit:

this

your best sniper player should be offclassing

a lot of the time its easier for a scout to sac (especially on granary no idea why people bomb roamers in cause that map is a giant spam box)

It's situational. Some maps I far prefer a roamer to offclass (via), others it comes down to specific points. On something like gully last it's almost always better for scouts to change, but on something like gran/proc sometimes a roamer changing to heavy can be good as scouts have a lot more room to do work.

go spy

something something jukebox

I personally think this.
1. Your best sniper should offclass.
2. Your roamer should rather stay on solly if he can help it because you can defend flank easily defend flank and you can do more with two soldiers than two scouts.

Oops small typo but you get what I mean. I am on a phone lol.

remember tek used to offclass sniper and mike was taking the pocket role while he was doing it, didnt happen too often though, but it worked everytime

roamer should offclass to spy tbh, sniper blows

Its very situational too. Once a spy go deep there is almost no way of him coming back alive, while sniper can just play passive close to spawn and switch immediately when needed.

If you're a good spy you will never fail a play. 100% conversion rate.

you have to remember that soldiers are often really useful at holding chokes. on places like snake last/gully last you'd definitely want to keep the soldier.

as above though i'd argue making sure your best sniper plays is usually the best option (unless you have 2 pretty good snipers in which case share it out i guess, but make sure that you dont end up running permasniper). on certain maps (like viaduct) me/the other soldier often play scout if our scout is sniping since its better imo to have a more mediocre scout combo than a mediocre sniper

It depends on the map. On some maps giving up 1/3 of your spam in a bad idea, especially when holding last. If you are holding their second however that spam is not as valuable and having your roamer snipe there is fine. IMO

if u play soldier outside of midfights you're doing it wrong tbh

This is mostly how I feel about the question as well.

Your roamer may not be the best sniper on the team but he is still the best choice to off-class because taking a scout off the field for defending 2nd point and/or pushing to mid does handicap your team. Scouts dominate the game, there are few reasons to take them off the field willingly.

Mackey roamer is the best roamer.