After playing both FE1 SNES and FE4, I fell in love with how simple the weight system was in those games. Higher tier weapons simply reduced your speed appropriately to avoid massive damage doubling situations. There was no need for pre-attack subtraction either (at least in FE1 SNES), your attack speed was listed in a units info, meaning all you had to do was check for who had 4 more attack speed than the other unit.
I hated the constitution system for it's permanent handicap to certain unlucky units, as well as requiring obtuse calculations if you wanted to plan multiple turns ahead. The Tellius games had essentially no weight system at all past a certain point, making it a forgetful feature throughout both games. 12/Awakening's removal of weight resulted in weapons being balanced out purely by required skill rank and HIT stats, which hurt magic especially hard. (Those poor useless wind tomes..).
The removal of weapon durability in Fates was an attempt to give the more casual player-base less to worry about, but the obnoxiously specific and sometimes convoluted nature of weapon-specific special abilities and debuffs do more harm than good, if you ask me. Every single shuriken gives a slightly different debuff. Throwing weapons lose double attack speed, but it's never listed on the stat menu when one is equipped. SIlver weapons went from reliable, but fragile, rare, high power weaponry that eventually made iron less important as you approached the endgame (a natural progression, with iron still being a just-in-case weapon), to a weapon most would honestly not even spend gold purchasing! And this isn't even accounting for all those crazy character weapons.
Even after playing through all three routes, I still have to spend time tapping each weapon (especially daggers/shruiken) every so often just to check what they do. It was annoying back in the GBA constitution days, and it still is today.