I was thinking an alternative to the MEDIC shout being used at full health would be having a second clip that plays with full health instead of less than full health, with the class saying something like "I'M GOOD!" or "THANK YOU!" when at full health.
I could already imagine Duo saying "thank you", so maybe not for taunting, but if the class goes from the "wounded" state to the "full health" state, I guess something like this could play for sure
In the heat of battle, you don't want to have to repeatedly aim at different players (sometimes unsuccessfully due to the unintelligent homing of the beam) and tap alt fire just to figure out who actually needs healing. You want to be healing the wounded ones immediately, as fast as possible, and you don't want to waste ammo, either. It definitely does not cost 0 ammo to check people, and those little bits you spend add up when you have to check multiple people or have a hard time actually hitting them with the beam.
Speaking of which, I should mention that as bad as a medic might have it when it comes to communicating with other players and evaluating their needs, engineers have it far worse. There's absolutely no way to tell who's low on ammo or got stuck with a poor weapon selection, so you pretty much just throw stuff at people and hope it's useful somehow. (Because like I said, people don't want to use the chat and leave themselves open to attack.) Pretty much the only sort of strategy you can make use of is to follow around a skilled player and keep him well-supplied, but it doesn't feel like much.
The behavior of the beam is to home into any player, but don't heal bosses of course. It has its good and bad points ; yet if it wasn't homing it would be impossible to heal anyone "in the heat of the battle" because there is no time to fire it accurately. I know it definitely doesn't cost 0 ammo right now, that's actually an idea I proposed for the future ; with a fast fire rate, the heal test (tapping altfire) could be fast and useful even "in the heat of the battle" (and assuming you keep an eye on the players fighting) -- and, being able to directly see the player's health in your crosshair seems to be a complex thing, I don't even know if I can code it .//.
As for Support if I may say... running out of ammo is very scarce. Usually you die before you used your 5 WTanks (3 to 5 starting weapons + 5 Wtanks for a single survivor is quite a lot, + an Eddie on occasion). Auto's support is not as much relevant as Roll's ability to heal : as you don't mandatorily need any weapons to survive, but ; you need a bigger health to have more chance of surviving.
are there really "poor weapon selections" ? Everyone gets common weapons like Tengu Blade, Fire Storm, Gemini Laser but you will never get rare and powerful weapons like Astro Crush or Sakugarne. I think the weapons are different but I'm not sure how you can say they're "poor", each weapon shines somewhere
Assuming the Auto is a serious/skilled player, he'd understand if you say a simple "wtank pls" in chat ; most of the time Autoes drop a weapon when their bar is full, even if nobody is around (so they can charge the next weapon)
Some Autoes even build their shop somewhere so you can ask him nicely a wtank without expecting the hale to find you here ; but hey anyway running out of ammo is veeeery rare, and even though, Mega Man is the only class that has a awful buster to fight with, all the other classes have a better Buster. Also don't forget you also get 5 new fresh W Tanks when you're the last survivor