I really don't see what use it is to deny that Farage has any sway at all. He clearly does. I've got no love for the man because I think he seems like a grubby opportunist who starts fires to gain influence. But he's clearly an extremely intelligent and effective politician who has achieved an awful lot with very very few resources in a manner that is pretty much unprecedented. Pretending he doesn't exist or can't do anything clearly is not going to work.
Re: the OP, I think the important difference with Macron is that Macron achieved his victory under a very different (i.e. much fairer and basically functional) voting system, which the UK doesn't have. The reason the SNP was able to quickly ascend to third party status is because they had support which was highly concentrated geographically - the key to winning under FPTP. It could well be that UKIP/The All-New Farage Party threatens to suck up votes from both Labour and Conservatives as they did in 2015. But Labour also has a more populist leadership than it did at the time, and we don't yet know who the Tory leader will be in the next election. At the very least, the Tories will surely be very wary about making concessions to their right wing, because it backfired on them so strongly under Cameron.