Firstly voting habits in by elections and General Elections are entirely different.
Tactical voting isn’t new. There was no tactical vote in Wakefield, they were always going to lose that one. Incumbent parties have always lost big majorities, mid term, with national issues and poor leaders.
I reckon the big Tory majority will collapse at the next General Election, but not because of tactical voting. There are very many Conservative MP in red wall constituencies on tiny majorities who will lose.
Hung parliament is my prediction.