What I mean is that the ability does not scale well. At first level it has the potential of being a full heal, at second level a half heal, and so on. I can't argue that its a free heal that you always have and that is never not useful, but personally I haven't found myself getting any clutch uses out of the ability outside of the first few levels.
We do not have a healbot in our party (Battlemaster 4/Cleric 1, Warlock 5, Sorcerer 5, Bladesinger 4/Sorcerer 1), but maybe we have been fortunate in that the casters blast everything before it does too much damage.
I actually used Second Wind for the first time in awhile last session to top myself off after triggering a flame trap. Although I felt we were about to have a Short Rest, I mainly used it to conserve a HD use.
Apologies for not being clear.
I don't think the argument "it scales badly" is a good argument for something being bad. Not by itself. If, however, the "bad scaling" leads to uselessness, it would be another story. But I just don't see that as the case here...
A Second Wind that provides a full heal at level 15 just as at level 1 would be very powerful, with large ramifications for the worldbuilding (fighters never stay injured for more than an hour at a time). Even the current Second Wind fully heals a 200 hp fighter in 8 hours flat.
But even with those campaign world issues aside, not every ability need to be Action Surge.
Action Sure is probably the most pure and well-scaling ability of all of D&D. At second level, it lets you take any action available to a 2nd level fighter. But at twentieth level, it lets you take any action available to a 20th level fighter. It is perfection. Scaling is flawless. Flexibility without limits is flawless. Absolutely the shining crown jewel of all of 5E design.
But while Second Wind is certainly not as strong an ability, it is not because of how it scales we should rate it.
I can understand, on a theoretical level, your argument. It would, in one sense, be more "elegant" if the ability always provided you with, say, 1/8th of your maximum hit points.
But not really. That would actually be a worse implementation in my view; needlessly forcing you to make a calculation in order to achieve a "pretty" rule. As well as being worthless at low level... In actual fact, the difference between being at maximum hp and close to death at low level is so small, it's not so overpowered to allow you to go from the latter to the former. After all, a monster can still bite your face clean off with a single chomp.
But at high levels, having hundreds of hit points means you seldom reach critically low levels, and for Second Wind to negate that vulnerability would be as overpowered as inappropriate. The Fighter has passed the phase where it needs the "crutch" of a Second Wind.
And a 20 hp free heal is still better than many heal-ups you have to purchase for money. The ability's usefulness just goes from short-term (in a single fight) to long- or at least medium-term (in a single day).
