Huh, that's actually a really good explanation of where the 10:3 balance standard comes from. I personally consider the point of balance to be approximately "enough nightplay information to confirm three players, plus a small amount of help from setup speculation". Your standard of "one mislynch, plus one scum found" is three confirmations exactly (a mislynch is worth two, finding a scum is worth one), but they're confirmations which are above-averagely useful (explaining why you didn't need to give town that small extra boost). So our balance rules are very similar. (Mine's a bit more flexible; it has to be due to NRG work, meaning that I need to assess the balance of setups which might not have been designed in a way that I'm used to.)
i assumed everyone knew that was where it came from. standard rule for setup size, if town has a decent amount of power, is n+1 mislynches to game end (n lynches to lylo) where n = number of scum (so 4:1 - eg dethy, 7:2 - eg newbie game, 10:3 eg standard mini, 13:4 e.g. standard smaller-sized large, 16:5 standard mid-sized large, etc)
(obviously lots of exceptions depending on mechanics/power and that's only for single scum-team setups but that's a fairly basic design rule i think - include enough town power to catch about half the scum team (or half minus one) and give town enough mislynches to catch the rest, or if you don't want to give town too much power, give them numbers)
(it also means scum requiring one extra lynch than town for a "perfect" win, assuming no extra killing roles, in relation to OP's idea on balance)