Reform (and the Greens) face one massive problem though: incumbency advantage. Neither party have many MPs at all whereas Labour and the Conservatives have lots. People know the incumbent and unless they're very unpopular this gives them a starting advantage. Where there are two potential rival options, the support of one (ie not the incumbent) is going to get squeezed, especially if there's an anti-Reform vote. There's so much information on the Internet now so it's easier to vote tactically. There was loads of this at the last election.
Take for example Walsall and Bloxwich, won by Valerie Vaz of Labour on 33% of the vote. Other candidates were Ind 20%, Reform 19%, Conservative 18%, Green 6% and Lib Dem 2%. The electionsuk forecast is 'safe Reform'. You would expect Reform to scoop the Tory 2024 vote. But you'd also expect the Green vote and perhaps the independent vote to take fright and switch to Vaz to keep Reform out.
Or South Suffolk, also predicted Reform, at the last election Con 33% Lab 27% Reform 19% Lib Dem 13% Greens 8%. Unless the sitting Tory MP is hopeless he'll at least be familiar and to win the seat Reform have to take his vote. You could even have a split vote on the right and Labour taking the seat.
There were also a lot of stay-at-homes at the last election. Possibly they could turn out next time for Reform but I bet they won't.
There's a very long way to go until the next general election and it would only take a modest recovery in Labour and Tory support to result in a Parliament just like the current one.