DnD House Rule Idea to Speed Combat: Max Damage!

Combat is DnD 5E tends to drag a bit too long due to HP bloat IMHO.  

A goblin had 4 HP average in B/X ( 1 HD -1) versus  7 HP average in 5E. An adult red dragon had 45 HP average in B/X (10HD) versus 256 HP average in 5E.  A 6th level fighter with 14 CON had 33 HP average in B/X (6d8+6) versus 50 HP average in 5E (6d10+12 w max at lvl 1).

Meanwhile, damage has not increased at quite the same rate. A 5E fighter has a higher STR damage bonus and feats, but is still only doing maybe d8+5 instead of d8+1. A  red dragon bite did 4d8 (18 avg) in B/X and does 2d8+2d6+8 (24 avg) in 5E. Consequently it just takes more hits to settle each combat. 

Proposed house rule solution: Max Damage!  The "d" in "d8" no longer stands for "dice." It stands for "damage." If your longsword does d8+2 including STR bonus, you always do 10 damage, or more on a crit. No damage roll. Same for monsters. The adult red dragon does 20 damage with claws, instead of rolling 2d6+8. 

To keep things fair, higher level spells should do a bit less than max, because the probability of rolling max on multiple dice is much lower, so giving spells max damage would make them deadlier relative to weapons. So I propose that spells of spell level 3 and higher should do 5 pts per d6 or 6 pts per d8 or 8 pts per d10. Example: red prismatic ray (8d10) would do 8x8= 64 damage. Fireball (8d6) would do 8x5 = 40 damage (unless the target saves for half damage of course). 

Higher damage will chip away at everyone's hit points faster. You also save the time spent actually rolling. It should be balanced since it is the same effect on friend and foe. 

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