Actually a lighter client can be made.

This is the client when i just login. After few minuts of play it can reach 400, then i have to close all others programs if i wanna play it. If i keep other programs open, the pc start to lag badly, everything i do.
Is a portable pc and this game is a java client. Older games with more features don't lag. I can play all the "age of empire" or mhytology online without suffer any ram lag, and you can see that the features between both games are pretty similars. Lotf of beasts, trees, objects, stats, players, charas, around the map without any ram lag.
If we can't fix the server, at last the client can be.
A light client don't exist? Prolly.
It can be done? Sure.
This is the proper answer. Now the op should search someone that love code H&H clients. Or he could just surrender that no one still coded it (because is a pretty big work).
Optimize the game is harder than code a bot, programmers prefer add features instead of fix the client coding. Everyone code what they care most, of course, but ther's no way that a light client isn't possible.
Simple, no one wanna code it.