I'd be fine with more base ad or something else, but I think you can't just straight up buff the debuff. Every bit of that debuff gives him AD, he gets part of what he steals. To justify it he'd have to be weakened in that aspect because if you debuff AND buff more, you're creating a big stat difference. He's had to get nerfs at points because of the power behind his Q.
As someone who played Trundle here and there back in S2 when he was an ugly disease monster and enjoyed his rework to a point (Mainly jung), I've always loved the pillar. His Q combo is fun but other than the debuff it wasn't any different to any similar reset ability. The rework's minislow was a great addition, but now its both a stat stealer and a slow so he has a lot of power budget in that move.
However his most interesting interaction is his E. Its the one longer range cc he has, it slows to setup your bite, you can wallpin or trap with it, or you can use it as a knockup. Its a long cd as a risk so the pillar has to be used smart. It was even good enough to justify him as a support in patches! Honestly if anything was buffed about Trundle that'd make him more interactive and give him a place in the meta, it'd be this ability. His Q will always be at least a little good since its a reset and can be combo'd with any amount of ad or onhits to give him damage spikes. His E though is pretty small and risky, maybe having a longer slow range or something would help?
as well as that all stats and health reduced from the enemy go to trundle as well.
