I think you are doing something wrong. I have a light app and very heavy SPA (written really badly with almost 5mb of code, D3 + Highcharts). Still, both app loads in less than 4 seconds in IE 11, FF, Chrome and Safari.
It does some fairly heavy image manipulation in web workers using typed arrays. The app loads a little faster in IE (the code comes in just under 1mb), but the runtime of my few test cases are magnitudes slower.
I do, and the page load for a big table is stunningly way over 10s even on Chrome/FF, while immense on IE11 (never tested EDGE).
Of course a simple fix is ReactJS or natively rendering. However due that only 6 Tables are slow and they changed barely we won't fix that, yet.