>The cash drag (assuming no fractional etf shares) will more than make up the ER difference until there is a sizeable sum invested

Remembering some quick math I had done months ago, it was hundreds of thousands.

However, I think I have heard of Vanguard doing a rollout of fractional Vanguard only ETFs for at least some users.

Other factors can still be more significant than the 1 basis point difference.