There is an article about Forczyk's book in the November 2016 issue of BBC History Magazine. He states that "Many of these were armed with 20 mm flak guns and bowitzers......And wbile the German navy had few deztroyers to deploy in the Channel, it did have large numbers of light warships to protect the barges from attack."
It's one of those technically true but somewhat misleading statements (see sitalkes numbers above). I suspect he's also ignored British vessels equivalent to the German escorts (motor torpedo boats, armed trawlers, purpose built minesweepers, the first Flower class Corvettes and various sloops) to make the numbers look better for the Jerries. And of cause, there's a certain qualitative difference (12 knot trawlers cannot easily concentrate to intercept a determined attack by two or three 35 knot destroyers)...
He also states that tbe "Royal Navy would have been lucky to intercept and destroy even 10 per cent of the invasion force." The RAF would have been "unable to deploy in strength until the morning of the landing."
Given the time it'd take for a 4 knot convoy of barges to get from Antwerp to the landing beaches, there should be plenty of warning for the RN to intercept, the RAF is limited mainly to daylight ops so morning of the landing is probably right for effective intervention by the RAF.
Of cause 'only' 10% irreversibly sunk mid-Channel may not sound like much (and given shear numbers on the German side doesn't seem that implausible), but that's units at least
decimated (in the pedantic sense, probably worse losses, not necessarily in terms of dead but more in terms of failed to make it ashore, once you factor in the badly shot up and turned back; got lost and turned back and badly shot up but made it across counts) before they make landfall. Worse than that, it's convoys disrupted, scattered and likely heading for the wrong beaches; command structures disrupted (Colonel X dead, Major Y on the wrong beach etc.); vital equipment lost or landed in the wrong place... 'only' 10% losses in the crossing still makes things horribly difficult for the Germans. I'm not sure Foczyk realizes that (or alternatively conveniently ignores it...).
Edit: There's also going to be losses during the landing (maybe not that many sunk, but barges grounded or overturned... salvageable once the area's secure but still out for at least the next few days) and the RN gets more bites at the cherry. 10% of the German vessels sunk on their way over plus, say, 5% sunk on their way back, repeat for the next wave... it's not that long before you're talking cumulative naval losses north of 30%...