Fighters and marksmen are the two worst designed classes in league.

tldr;

marksman and fighters are poorly designed because 1)they need to many stats to succeed 2) league was not made with turn-rates like dota and as such if we are to have both classes be AA reliant we need to have the differences between them become significantly more extreme so that abuse of items is less likely to occur.

Just needed to say something to clear my head.  Be nice if someone from riot heard my theory.  Anyway, fighters and marksmen are the two worst designed classes in league.  My reasoning comes down to stats and items.  First, let's look at the well designed classes in league:

Tanks-HP, AR/MR, hp regen (regen is more of a luxury than a necessity)
Mages- AP, mana
Slayers (assassins) - AD/AP, lethality/?mpen? (mpen isnt that common but is still useful)
controllers-- basically the fancy reject mages also some random tank/fighters like blitz taric thresh etc

While these classes can be OP, it is easy to tell when they are because only a handful of things will be excessively powerful.  
Tanks will typically do too much damage for how much survive-ability they have, but you rarely hear people complain about tanks surviving too long without it being accompanied by doing too much damage.  
mages biggest problem comes down to how reliant on mana should mages actually be.  Also more raw ap items and %pen would be nice
slayers- mpen is weird since riot didnt do the whole lethality thing and bring in some items but overall they want pen and raw damage

Now, lets look at the semi messed up class of slayers or the reject fighter club: http://leagueoflegends.wikia.com/wiki/Slayer
they are
yasuo, yi, riven, fiora, jax, tryndamere, kayne

All these champions, similar barring jax, are similar to assassins in that they want raw AD and lots of it.  Yi also wants on hits while riven and fiora would like hp and trynd and yasuo love crit, but they all build a lot of raw AD when they can.

Now why are marksman and fighters terrible?

marksman need: AD, AS, crit, pen, LS, MS, 
Fighters need: AD, AS, HP, MR/Arm, on-hit, MS, regen/LS

In short, both classes need waaaaay to many stats to succeed.   While this can be argued as OK for marksman since they scale so well into the late game this is not as reasonable for fighters.  One of the most common items found top-lane among fighters is something that builds out of tiamat either TH or RH.  because tiamat gives innate regen from its bead component, BOTH items give you more regen.  This means getting AD, to some extent, and regen is intrinsically somewhat do-able.  The two most popular followups on these items are trinity force and black cleaver.  Those who build cleaver, darius, J4 etc are more caster oriented with the exception of olaf who has massive built in sustain and AS, everyone else, irelia, jax, etc need AS which is why riot can never make a new fighter item.  They always quote something like "...marksman would abuse it..."  which brings up the fundamental problem.  Marksman and fighters are TOO similar in design.  I cant remember where, but vairous rioters have noted that fighters were supposed to be the melee carry equivalent of marksman.  This is because league is based on DOTA and thus was technically envisioned to have melee carries who were equivalent to marksman.  However, with the removal of turn-rates this was made virrtually impossible.  This is why yasuo is partially why yasuo is so hated.  He was designed to be a melee equivalent to marksman, but he just needed waaaaay to much to make that happen.  By the time yasuo was created the game was fundamentally incapable of truly balancing a melee equivalent to marksman. 

So then what does this mean?  It means fighters need to be redesigned to NOT need as many stats as marksman so that they can get new items without marksman auto abusing barring ez because Ez is ez and will abuse everything.  What I propose is that fighters reliant on aa like irelia, jax, xin etc need to get their as buffed in kits or base stats so that figher itemization does not need AS in it.  Also, marksman in generally should have their scaling AS reduced to almost nothing and have their itemization have more AS and AD in it.  what would an EXTREME version with nonsensical numbers look like? 

fighters get ~ 2.0 AS through base kit and highest in game armor and MR while subsequently getting lowest HP in game
Ex: Jax now gets  up to 2.0 AS from his kit and base AS trinity gets stinger and AS completely removed.
so 6 items -boots would be tiamat upgrade, 4 other HP/AD items and maybe one ARM/MR item.

marksman get higher base AS  and significantly lower scaling and get those stats from items
EX: Sivir gets like 0.5 AS from stats, IE goes up to 4k flat and gets 100+ AD crit, and AS all in one item.  last whisper items now get AS as well.
ALL items at full build now give AS.

what does this mean?  Fighters now build AD, HP, MS, regen On hit items with no AS attached.  no longer build MR armor or AS.
marksman now need 3-4 AS items but can get them more easily.  Now bear with me this is an extreme example (only thing im sure of are these numbers suck), but it is to illustrate that now marksman will stay approximately the same but now have less ability to abuse items in other classes.  And if they do opt to pick up a fighters item it will be a significant trade off.   Also, the addition of another tree in the runes section to help fighters more than marksman could be a nice way to achieve this but now i digress.  That is a whole other topic, however, and something I am not as inclined to discuss because I havent played since the new runes have come out.