NO. I don't know what terrible things happened to you at EWR but it will only be worse at LHR. Summer storms, labor problems, lost and stolen baggage, massive crowds, ATC delays... avoid LHR at any cost.

The EWR transfer would be better, and the JFK transfer on DL/Swiss would be a little better than that (though both airports are delay-prone).

Better STILL: MEM-AMS-GVA on NW/KL. I don't know why the above poster suggested you avoid AMS, it's the smoothest transfer point in Europe.