As others have noted, the problems are with specific ISPs and their underdimensioned last mile network and/or backhaul. A modern submarine cable, like Google's

As others have noted, the problems are with specific ISPs and their underdimensioned last mile network and/or backhaul. A modern submarine cable, like Google's new Dunant transantlantic cable, has 250 Tbps of bandwidth. For reference, the largest Internet Exchange in Europe, DE-CIX, just reported a new traffic record of 9 Tbps. So, no, anything using fiber isn'ta bottleneck. You can fit all of DE-CIX traffic on a single strand of fiber with off the shelf gear.