That was 6 months out from the election. These polls had Clinton trailing, badly in some cases, yet he won. The problem is always the staying power of these 3rd party candidates. Sometimes they poll well, but as elections draw near most voters tend to gravitate back to one of the major parties - if for no other reason than to block the party they like less.
Perot dropping out and sabotaging his own campaign, as you’ve mentioned, shows precisely the kind of erratic behavior that SHOULD have prevented so many well meaning right of center voters from wasting their votes on him and throwing the election to Clinton.
If Trump ran as an independent all he would do is pull some % of right leaning voters. It is nonsense to think, in a country as politicized as ever, that Democrats, “moderates”, Hispanics, minorities, etc, are going to vote for Trump. It is also nonsense to think Trump throwing the election to Hillary would teach the GOP some kind of lesson. Neither 1992 or 1996 taught the GOP anything in particular, heck they ran Bush the “compassionate conservative” in 2000 and managed to win with it.
The only point I'm making, or debating, is that Perot had raised the issues and won the support that could have won the election for him had he not sabotaged his own campaign by dropping out.
The same sort issues and opportunity exist again this go round, and Trump has an excellent chance to win if he runs a smart campaign on the issues he's raising. Whether he will run that smart campaign throughout the process remains to be seen. But he does have winning issues.