"Going forward, we will regularly evaluate the Alchemy metagame and release additional balance adjustments to keep things diverse, fair, and fun," it reads
R&D probably demanded the "can't play lands" clause as a nerf
It is a clear, measurable, motivating goal
All in all, milling your opponent out isnt a particularly great strategy, and lets face it: there are much better cards youd want to play than Trepanation Blade
When you cast Radiate in response to a spell that targets a single permanent or player, you copy that for each possible legal target
And you only have to get to a total of 20 creatures, lands, and artifacts once to win - at that point you never have to let your opponent take another turn, and can just keep casting spells and generating tokens, freeing up more and more of your board to attack