Scaling for a class with Extra Attack comes primarily from Extra Attack.
So a reaction that gives you a single attack is simply not scaling for them. Reactions thus become less potent, relatively speaking, as they level.
Sure.
For a low-level character who gets one attack, that's doubling his DPR, for a high-level one getting 4 attacks, it's +25%. I see a potential issue with that, but it's that it's dropping off in impact as you level.
Yes, it is a feature. It adds X DPR. It shouldn't multiply DPR by X.
As you gain levels, you gain more features. Each adds X DPR every ~Y levels.
Then, you end up doing K + Level * X/Y damage. Damage scales roughly linearly with level. (K is your damage without these features)
If you have a feature that multiplies DPR by X, you have to make it really weak at low levels to make up for its large impact at high levels.
If you have a feature that multiplies your damage by X every Y levels, you deal (K * X)^(Level/Y) damage. Damage scales
exponentially with level.
Now, if K + Level * X_+/Y = (K X_)
^(Y/Level), where X_+ is additive damage and X_ is multiplicative damage, and Level=20, we get:
Plugging in K = 8 (base damage), Y = 2 (feature every 2 levels), and level is 20, and X_+ is 8 we get:
8 + 20 * 8/2 = (8 X_*)^(10)
11 = X_*^10
X_* =~ 127%
So getting +8 damage every feature is the same as a feature that grants +27% damage per feature, at level 20. But back at level 1 or 2? +27% damage was about 2 points.
Now you can have those multiplicative features. But because 5e wants hero damage to be roughly linear (well, affine), and scaling damage is polynomial or exponential, you cannot have too many of those multiplicative features.
My attempt is to ensure that these "warlord-ish" combat styles are strong (even stronger than the base ones) when you get them, and don't scale ridiculously. Sadly, even after these heavy restrictions, they look like they could still be too strong; an extra tap (which many of these reliably are) at the cost of a reaction is too strong for a combat style - it leaves duelist in the dust, even at level 20.