Well unless you were happy to have had UKIP in government, or constantly very hot on the heels of the two main parties, then it wasn't ill-conceived at all. It was a calculated risk that with hindsight, didn't pay off. Mainly because the Remain campaign was absolutely dire and focused almost entirely on insulting Leave voters and implying over and over that they were little more than a bunch of low IQ gibbons on crack, rather than on the perceived benefits of staying in the EU.
DC had obviously hoped that a referendum would put the whole thing to bed once and for all. He miscalculated. But if UKIP had won an election, or at least won loads more seats in Parliament, you'd have got a referendum anyway eventually. DC just made it happen sooner.
Now, as a result of no government yet managing to make a decent fist of things post Brexit and no government managing to get a handle on immigration either, it looks like you are still going to get Nigel Farage as prime minister. It's just that the party is called Reform now.
If Brexit and immigration had been managed better in the years since we left the EU then Farage would probably be putting his feet up in retirement in Spain by now, a single issue activist whose work was done, and Reform possibly wouldn't even need to exist.