I don't see how that's a problem. Those who want subs immediately after the show has aired get a good translation and decent video quality, while those who're willing to wait for groups like Commie, Underwater or rori get the same professional subs with typesetting, better video quality and song translations in a shorter time frame than doing it all from scratch.
Not to mention there's no real shortage of fansub groups who translate from scratch. There are four groups subbing Tamako Market, three even for such a difficult show like Nekomono, and three even for garbage like Senran Kagura. Excluding maybe Hadena and SubDesu, all of those groups are leagues ahead of what would've been considered amazing just a few years ago.
As for the illegal aspect of improving simulcast subs; all fansubbers consider themselves no better than warez groups or the live action movie scene, regardless of whether or not they're subbing licensed shows. The days of fansubbing being considered free advertising are long gone. Fansubs are going to exist as long as people don't want to pay for an inferior option. Even the very best simulcast service, Crunchyroll, is still inferior to downloading a HorribleSubs rip, because there is no option of downloading Crunchyroll's streams. If you have the money to pay for a Crunchyroll subscription, then go ahead, because no-one will argue against supporting the anime industry. Please just keep in mind that there are NEETs like me who simply don't have money, and without fansubs and fanrips, I wouldn't be able to watch anime.