or why dont make individual stats buyable for gold instead of items but you can spend a maximum of 18K gold on stats/effecs/actives.
also there will be always "the best item" for one particular champion to buy. ofcourse you could say "different items for different situations" but that doesnt affect the first 2 or even 3 items very much because these so called "core" items are simply what support the role of the champion best. what makes trinity so good on irelia is not that it buffs her auto attacking with her true damage so super much but that it gives her alot of speed and allows her to Q casterminions (applies on-hit effects) from full hp and melee ones from much higher hp than usual to dash while getting the Q reset immediately aswell as crazy speed from the phage passive.
now if you make items very similar and only change minor things like the static shiv/rapidfire cannon thing, you will have "THE BETTER" item every time since it is better in the more-likely majority of situations and ONLY if you make an item that is VERY SPECIALIZED on one specific thing you want to do (hold towers/waveclear, splitpush, assassinate squishies, duel bruisers, kill tanks etc) only then you can really have an item diversity that allows you to adapt to situations.
for example, zephyr was a very good item because it was excellent for splitpushing on some champions and even tho it wasnt bought very often, it fulfilled its purpose. it couldve been tweaked to be even better for splitpushing and even weaker for fighting, for example by altering its buildpath into recurve bow + phage so that its final form doesnt have the CDR anymore but gains the phage passive instead. stuff like that.
also there could be an item that absorbs a flat amount of damage from every source of magic damage taken so you can effectively reduce damage from dots and magic DPS. there could be many different items with cool effects that are very situational but only this way you can really create item diversity.
there could be items that have extremely strong raw stats or items that have almost no raw stats but very strong effects. there could be items with spammable effects that have extremely low cooldown.
this could be a much more interesting game but instead we have every heavy AD item cost the same and give almost the same, we have static shiv and static shiv 2.0, we have two versions of lastwhisper that both suck. everything gets standardised so that there is always "the best build".
for example, the best build on shyvana jungle is devourer trinity deadmans plate. only if they are ridiculously full AP like brand support, fiddle jungle, lux mid and lissandra top you would swap deadmans for spiritvisage but in every regular game you would absolutely get these three items and then adapt.
as a jungler, you are allready somewhat forced into buying a jungle item and then you only got to choose from 4 different ones of which you mostly cant even use half. it would be really cool if there were like 10 different jungle items so you could really ADAPT situationally but no, they want every champ to buy the same jungle item every game and the only variation some fighters have is to get cinderhulk instead. well AT LEAST THAT.
seriously, riots item philosophy is shit. plain shit.
and 
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. It would gain a bit more attack speed, attack damage, and some OnHit magic damage but lose the crit chance and the %Movespeed (sads). Most importantly, it also gains the Phantom Hit named passive, which procs when you use Spellblade. If a champion picked up Trinity and Devourer for some reason, the Spellblade version of Phantom Hit would be disabled.
into the Crit/Spellblade item. It now builds from 
