lighthousei understand all the arguments you gave but i think youre exaggerating a bit, its not like this weapon changes the medics hud to show the enemies health and uber at all times.
your medic first has to have an actual line of site to the enemy, and then has to track their mouse on the enemy long enough to look at the hp/uber (which really isnt hard of course but it could take a moment). if your medic is safely able to peek because the enemy is far away, that knowledge is not particularly useful, whereas if your team is close enough to be able to take advantage of that info, then your medic is putting himself at risk getting it.
You do have good points in your argument, the medic absolutely does not have immediate access to the health pools of the enemy players, however, there are many situations where medics could absolutely be positioned in such a way that they are safe/not taking any risks with their positioning, but the health number they are reading out to their teammates are at that moment incredibly useful. Most obvious example is midfights. Medics stay present with their team on mid fights, and it won't be difficult for a half-decent medic to position himself safely with line of sight of his enemies at the same time. Considering how much of an impact a midfight can have on the rest of the round, I'm hard pressed to find a reason why I wouldn't run solemn vow, if at the very least to mids.
lighthouseon top of all that for the most part your team should have a pretty accurate estimate of the enemies health and uber anyways. i think the opportunity to get 25% uber from a melee is arguably just as valuable as having to take a risk to maybe gather info that you might already have.
Again, it is possible that running out to peek an enemy's health could be considered a risky move, but it could also be a very safe and smart move. It depends on the situation really. However, if Solemn Vow were to get unbanned, the opportunity to get 25% uber from a melee would be considered so situational (as it already is, you could argue), that I have a hard time imagining medics perma-equipping (or switching to and from) the ubersaw for specific situations like those when they could play it safe the entire match and have constant access to the health, uber percentage and medigun of any enemies that crawl in their sights.