Your point is a good one in general, but it's a bit out of context here. The reason people always argue a sitting president in his/her first two years cannot be blamed for/credited with economic conditions is that, while certain "stimuli" (tax cuts and bank bailouts, for example) can cause immediate impacts, such impacts are typically temporary in nature. It typically takes two years for policy to affect social conditions at the Federal level, for better or for worse.

It's been about two years, right? So yes, except for the tax cut (which, let's be clear, ANY Republican president would have put through with a Republican majority in both houses of Congress) and the trade war (in which we're getting our a$$es handed to us), Trump should get no credit/blame for the economic growth during his first year (which is all but gone, just one year later, thanks in large part his reckless policies finally taking root).

Now that two years have passed, we're seeing the results of Trump's policies, and it's not looking pretty. The realities of the tax cut and the trade war are not looking positive these days, either. It wasn't time last year, but this year, it's time to give credit where it's due.