You are doing a wrong comparison.
Interlude l2j = crap.
You compare interlude l2off with l2j Gracia final.
Different software with different chronicles.
I have seen l2j servers with a lot of people, 5000+ and no lag.
It all depends on the admin.
I rather play on a simple l2j Gracia final server with an admin that knows what he does and that cares than on a interlude l2off server with an admin that just paid some files and opened a server.

I am not referring to me as an admin, but as a player.
I also suggest you try some descent L2J server to play. Those problems you mentioned are easy to be fixed and are not L2J faults but system setup related where anyone with basic IT knowledge can fix or prevent.
Playing on some crap L2J servers doesn't give you the right to judge the software but gives you the right to judge the Admins.

Show me one l2j server at the moment that has 5000 players.None.And no l2j has perfect targetting like an l2off.Its always very sluggish.