If, as Marx advocated, "surplus value" were returned to workers, how might this slow the economic growth and development? Or would it?

In simple words, the given case relates to the basic business principle of profit through reinvestment. Whenever, a company makes surplus profits , most of the time it reinvest it to keep competing in the competition or to grow itself with much cheaper capital source.

If the rule of Marx is followed,  the reinvestment will never take place and there will be no growth in the industries. Hence the economic growth overall will be hindered.

because he is that the right