You can replace D4 with D6, but not like this. Just reroll all D6 that are 5 or 6. Your options give the advantage to D6 in the 1 and 4 option and to the D4 in the 2 and 3 option. No equal outcomes even if you factor in the average.
If you took a system that uses D4, replaced that with D6 according to my table and didn’t tell your players that the system was actually meant to be played with D4, do you really think they’d notice any imbalance? Would it affect their fun?
No, not at all. You only notice a difference if you calculate it, it won’t suddenly make your character class or weapon imbalanced.
The fact that you’ve made it impossible to roll an 8 by replacing 2d4 with 1d6+1 might impact the game just a bit. Also with 2d4 a 5 is 4x as likely (1+4, 2+3, 3+2, 4+1) as a 2 (1+1) or 8 (4+4); with 1d6+1 all outcomes from 2 to 7 are equally likely, so you’re far more likely to get a critical hit or critical miss (if the game has that sort of thing, and you adjust it for the reduced range).
You can replace D4 with D6, but not like this. Just reroll all D6 that are 5 or 6. Your options give the advantage to D6 in the 1 and 4 option and to the D4 in the 2 and 3 option. No equal outcomes even if you factor in the average.
Throw 1 D4 please. Ok I got 5.
The difference is purely mathematical. It won’t impact any balance in game at all.
How is a 10% worse roll in case of 2D4 not changing the balance?
If you took a system that uses D4, replaced that with D6 according to my table and didn’t tell your players that the system was actually meant to be played with D4, do you really think they’d notice any imbalance? Would it affect their fun?
No, not at all. You only notice a difference if you calculate it, it won’t suddenly make your character class or weapon imbalanced.
The fact that you’ve made it impossible to roll an 8 by replacing 2d4 with 1d6+1 might impact the game just a bit. Also with 2d4 a 5 is 4x as likely (1+4, 2+3, 3+2, 4+1) as a 2 (1+1) or 8 (4+4); with 1d6+1 all outcomes from 2 to 7 are equally likely, so you’re far more likely to get a critical hit or critical miss (if the game has that sort of thing, and you adjust it for the reduced range).