TesseracT's last record sold more copies in the UK than anyone else on the Sunday outside of Sabaton.
I think you mean Friday, but either way that's simply not true. Powerwolf, Bodom and Soulfly all sold more than Tesseracts last album. Metal Church's previous album also got to number 25 in the chart, which should in theory place them a couple of slots higher on the lineup too.
Even going by Download 2018, Tesseract played in the same slot as Thy Art is Murder who are 2 slots lower on BOAs lineup which would be a more suitable position for Tesseract. Looking at European lineups, they're even lower than that, in a lot of cases they're on the 2nd stage, which again would be a better position for Tesseract.