YMMV but I call a lead of 290 seats and 2,879,791 votes a landslide.
It was the Lib Dems that seem to have taken most of the Tories' voters: 72 seats (up 64) and 3,519,143 votes. The latter at least checks out. Reform was up 1 seat from 2019 for 5 seats total. Not quite a big splash then.
Labour also won big in Scotland against the SNP for the first time in years (but that was rather the fault of the SNP).
Data from wikipedia: https://en.wikipedia.org/wiki/2024_United_Kingdom_general_el...
Labour got 9,708,716 votes in 2024 vs 10,269,051 in 2019. Starmer and Labour did not convince voters adn lost votes to the Greens.
What happened is that people did not vote for the Conservatives and instead voted Lib Dems and, especially, Reform UK, which got a massive 14% (3rd place and more than the Lib Dems). The Reform UK vote is because the Conservatives did not deliver on Brexit and even more importantly did the opposite of what they said on immigration, which reached record level.
The number of seats to Labour is a result of the above (Conservatives dropped so Labour candidate was elected) not because people voted Labour more than before. The surge is Reform UK.
So the same issues that have been at play in the Brexit referendum are still the key issues.
https://www.bbc.co.uk/news/articles/c4nglegege1o
Reform's seats came from the Tories, unsurprisingly, and like you say Reform won more of the popular vote than the Lib Dems (4,117,221 vs. 3,519,143; not a wide margin) but Reform also campaigned in many fewer constituencies where they didn't have to compete directly with the three largest parties (not to mention Lord Buckethead and the Monster Raving Loony party, their nemeses). So maybe they have lots of supporters in certain areas, but only in those certain areas.
Reform is not a serious political force in the UK. They only renamed themselves from The Brexit Party, but they remain a single-issue party that appeals to a tiny minority of voters. The majority of the electorate are much more concerned with real issues like the economy, the NHS, education, law and order, and the environment. Brexit wasn't even a particularly big issue in the last elections. Even the Lib Dems, who had campaigned for a second referendum in 2019, laid it to rest this time and focused on more recent issues like sewage spills in rivers etc.
Might I also hog the mic a little while longer to say that I, personally, am mostly socially conservative, and am absolutely appalled both at the Tories and Reform, who are nothing but right-wing populists and demagogues that do not care a jot about all the things that socially conservative voters care for: jobs, order, stability, lawfulness, the economy, family, etc. And let's not forget that it was Margaret Thatcher's Tories that got the UK into the EU, and did so because it was beneficial to the economy, trade, and the stability of international politics. Exciting the EU was exactly antithetical to conservative ideals: it was a radical act of self-mutilation.
Labour are now the conservative party, the party of business and fiscal responsibility (and sitting on your hands while you kick the can down the road) and that's why they took all the Tories' votes: because the socially conservative constituency got fed up with the Tories' antics and, the Brexit fever having passed, wanted to go back to order and stability.