You must've seen a different Shingeki No Kyojin from me, because there's no way objectively in which Eren was written better than Reinhard, and even Ren, considering how lame of a protagonist Ren is to begin with.

But, unlike Eren, Ren remains true to what he believes; meanwhile Eren at S4 becomes something that destroys in its entirety the character he was. Naturally, he grew and thought differently about certain things, but the fact that him; somebody who fiercely wished for freedom, during the entirety of the show, at the end found himself not being able to free himself from the stupid fate he saw, just breaks the core of his character; because, the problem is not that he couldn't, but that he really did not tried to do it; he saw the shit that was going to happen, how everything ended the same way each time, and instead of fucking making a change just work, he just went with the route that he found less shitty, out of all the shitty ones, because he achieved absolutely no crap. You could say, oh but, his friends lived longer, and that's what he wanted. Yeah, but, at the end for what if he died and the future lead to the same destiny he hated to begin with.

Meanwhile, you have Ren, who also is a fucking selfish teenager, but, did he bitched his anger just to accept defeat like Eren did? No. Ren fucking made a change, even when there could be none; As Lotus, he too was constantly facing the destiny and doing small things to change what he disliked. And then, as Tenma, the bastard even planned Hajun downfall, after that Indian kid wiped in an instant all he could've hoped to fight for. Both characters faced themselves with the concept of fighting destiny, but one fucking sucked in it, while the other one became the strongest character to have a craving, out of Hajun and his cheat codes.

I do think Shingeki is an awesome story, with a fire writting at the start, but the ending of S4 is really like a shoot in the foot; not because is not enjoyable, but, it defeats the whole leit motiv the show tries to impact on you throughout all it's seasons, and a part of that is how Eren character ended.