Is this arguably anticompetitive and illegal?

Nobody can even state that it’s actually happening “for competitive browsers” as even Chrome users are reporting an unexplained lag/slowdown. At this point, it’s just wild speculation and bandwagoning.

You absolutely can tell what's happening by reading the source code. They are using a listener and a delay for when ontimeupdate promise is not met, which timeouts the entire connection for 5 full seconds.

function smb() { var a, b, c, d, e, h, l; return t(function(m) { a = new aj; b = document.createElement("ytd-player"); try { document.body.prepend(b) } catch (p) { return m.return(4) } c = function() { b.parentElement && b.parentElement.removeChild(b) }; 0 < b.getElementsByTagName("div").length ? d = b.getElementsByTagName("div")[0] : (d = document.createElement("div"), b.appendChild(d)); e = document.createElement("div"); d.appendChild(e); h = document.createElement("video"); l = new Blob([new Uint8Array([26, 69, 223, 163, 159, 66, 134, 129, 1, 66, 247, 129, 1, 66, 242, 129, 4, 66, 243, 129, 8, 66, 130, 132, 119, 101, 98, 109, 66, 135, 129, 4, 66, 133, 129, 2, 24, 83, 128, 103, 1, 255, 255, 255, 255, 255, 255, 255, 21, 73, 169, 102, 153, 42, 215, 177, 131, 15, 66, 64, 77, 128, 134, 67, 104, 114, 111, 109, 101, 87, 65, 134, 67, 104, 114, 111, 109, 101, 22, 84, 174, 107, 169, 174, 167, 215, 129, 1, 115, 197, 135, 207, 96, 156, 234, 24, 157, 175, 131, 129, 1, 85, 238, 129, 1, 134, 133, 86, 95, 86, 80, 56, 224, 138, 176, 129, 1, 186, 129, 1, 83, 192, 129, 1, 31, 67, 182, 117, 1, 255, 255, 255, 255, 255, 255, 255, 231, 129, 0, 160, 204, 161, 162, 129, 0, 0, 0, 16, 2, 0, 157, 1, 42, 1, 0, 1, 0, 11, 199, 8, 133, 133, 136, 153, 132, 136, 63, 130, 0, 12, 13, 96, 0, 254, 229, 106, 0, 117, 161, 165, 166, 163, 238, 129, 1, 165, 158, 16, 2, 0, 157, 1, 42, 1, 0, 1, 0, 11, 199, 8, 133, 133, 136, 153, 132, 136, 63, 130, 0, 12, 13, 96, 0, 254, 232, 120, 0, 160, 187, 161, 152, 129, 3, 233, 0, 177, 1, 0, 47, 17, 252, 0, 24, 0, 48, 63, 244, 12, 0, 0, 0, 254, 229, 106, 0, 117, 161, 155, 166, 153, 238, 129, 1, 165, 148, 177, 1, 0, 47, 17, 252, 0, 24, 0, 48, 63, 244, 12, 0, 0, 0, 254, 232, 120, 0, 251, 129, 0, 160, 188, 161, 152, 129, 7, 208, 0, 177, 1, 0, 47, 17, 252, 0, 24, 0, 48, 63, 244, 12, 0, 0, 0, 254, 229, 106, 0, 117, 161, 155, 166, 153, 238, 129, 1, 165, 148, 177, 1, 0, 47, 17, 252, 0, 24, 0, 48, 63, 244, 12, 0, 0, 0, 254, 232, 120, 0, 251, 130, 3, 233 ])], { type: "video/webm" }); h.src = lc(Mia(l)); h.ontimeupdate = function() { c(); a.resolve(0) }; e.appendChild(h); h.classList.add("html5-main-video"); setTimeout(function() { e.classList.add("ad-interrupting") }, 200); setTimeout(function() { c(); a.resolve(1) }, 5E3); # <------------------------ 5E3 = 5s return m.return(a.promise) }) }