I hate to insert myself in the middle of a semiheated argument brewing, but I think there is a lot of misinformation or just badly misinterpreted things being said
This is something I largely agree with entirely those rules structures present in 3.x enabled all of this
and included room for the sort of let the gm decide unfilled space
@transmission89 (or at least some others) are advocating for in the 1e/2e style of some areas that were just brought forward largely void of rules in 5e with the one size fits all (dis)advantage system. that allowed the player to confidentially act with greater freedom backed p by the rules themselves do do things within the shared fiction feeling like they have at least some capability of understanding what the cause & effect will be. For whatever reason 5e chose to ignore that in favor of nu rules are somehow best rules & (dis)advantage is the perfect hammer in all situations.
Specifically that mechanic was the combination of two parts known as "the dms best friend" & "stacking bonuses]"/bonus types. A lot of hate gets applied to bonus types over how they
could be poorly used if you ignored the advice explaining not to in the rule itself, but if you
actually read those sections rather than kneejerk regurgitation of decades worth of misinterpretations (totaling less than a page
here) it's easy to see how it helps meet the needs of both osr ask your gm style & the more modern rules heavy. Not only that, it does so in a rules light easily extensible framework that can be applied to nearly any situation or simply tossed aside in favor of letting the gm make something else up.
The different editions did different things better & had different weaknesses. The +2/-2 & bonus types is one example, standardizing where bonuses & penalties kicked in on the attribute arrays in 3.x over the attribute by attribute from earlier editions is another. Having those arrays generally kick in with -1/+1 at 6 & 15ish rather than 8 & 12 is an area the older editions did it better by not making players feel so forced to use the most optimal attribute placements.
Actually crafting items in 3.x took a feat, (generally) someone having the ability to cast a particular spell, potentially unique ingredients, a boatload of gold,
and a nontrivial amount of exp consumption. If bob could craft a kickass sword because he took the relevant feat instead of powerattack or whatever good for bob. Being able to craft that badass sword didn't allow him to craft rings boots armor or whatever too unless he
further invested in even more feats to make becoming a custom crafted christmas tree all that more difficult.
You & so many other proponents of 5e''s choice to go with an
exclusive 3 attunement slot system as the only limiter are ignoring another important factor on magic item availability though. If I as the gm did not put a particular magic item out for the players to find it simply did not exist for them to put on their character sheet. That lack of existence was not something players could sidestep by going to a npc crafter/shop either because I as the gm still had the final say over what was available & what if any limitations or changes it had over PC buying hopes.
Attunement is a good system, but like (dis)advantage it should not be the
only system even if others are simply options for the gm to employ. Slot types & affinities was something that had value but getting rid of it means that I can't throw out minor magic items that don't need attunement due to not being worth attunement for +1 to baketweaving checks made on the deck of a ship in stormy seas even if that's somehow cool. 5e's perfect hammer for all situations tendency is one of its greatest weaknesses.