Not from England so take anything I say with a grain of salt
This seems like an election Labour would be better off losing. Brexit is going to tank the UK economy and they do not want to be at the controls when that happens. Best to let the Cons take the flak for it, and sweep into power in four years to rebuild
Brexit really is the greatest political cockup of recent times, more damaging even than Trump winning imo
Labour would almost certainly be better if they didn't win this, especially because it is very unlikely Labour would be able to implement most of their manifesto in what is potentially a financial crisis for the UK, however having Theresa "No deal is better than a bad deal" May in charge would dictate far far more than just the inevitable 5 to 10 years they would win after 2022, it is really quite hard to screw up a country more than leaving the EU without a deal, which is something that the Conservatives are in theory willing to do.
Still silver lining a screwed up Brexit gives Labour a better chance to win the next elections.
Also I believe you are seriously underestimating how much Trump has accomplished in just 138 days, he is clearly an over achiever as far as fuck ups go, so with still 1322 days to go (lets assume the worse), he might easily start a war in Korea killing dozens of millions of people in the process.
Part of me (don your tin foil hat) has always thought the tories want to lose this election for precisely this reason, they play the long game, throw this election, then in 5 years time clean up on a blame Labour for the Brexit shit and then people will never vote for them again as they destroyed the country, even though they instigated it all.
I think if they were genuinely trying they would have managed to lose (I know election not over but lol), and it would be a really good play, you would likely get a sane brexit deal, or well as sane as one can expect from such a situation, you would have labour take 3 years of the consequences of leaving the EU which will certainly not be nice, just for them to come in and claim Labour bended to the EU aka Satan, blah blah blah usual rhetoric, and lead for what is likely the next 2 elections.
OFC this is the party that claimed to go for hard brexit, doing comments about kicking out EU citizens, that started brexit in the first place, trying to ransom security cooperation and so on and so forth, so you know I think all around it would be giving them way way too much credit even if it mean they failed to lose the election on purpose.