Pen plotters could accept sheets of A4 and very precisely position them since at least the 80s. I'm surprised that dot-matrix printers didn't adopt similar technologies sooner, though it could be because by the mid-80s dot-matrix printers were the budget option, fanfold paper with the tractor strips was still abundant, and it was much easier to just stick with the cheaply manufacturable technologies rather than take the risk of innovation with a product that wouldn't sell upmarket anyway.
Were A4 plotters that much of a thing? I'd thought plotters were usually larger format (A0-A2 sort of size) for engineering drawings etc. Also iirc they were insanely expensive compared with your standard microcomputer dot-matrix printer.
The most popular pen plotter, and sort of the "holy grail" among hobbyists for this sort of thing, is the HP-7475A, a desktop model which could accept A4 or A3 sized paper (or US A or B size). It cost $1895 upon release in 1984, so yeah, pretty expensive when compared to the $650 an Epson MX-80 (best known dot matrix printer) cost. But there was so much more to the plotter than its paper-feed technology; it was much more a precision instrument in a variety of ways.
Dot Matrix are still used in outdoor / high humidity environments in USA.
A lot of car shops with regular 100% humidity conditions will swear by dot matrix + tractor for feeding paper + printing. Plus, the carbon copy forms are guaranteed to be exact carbon copies which also leads to legal guarantees about copies of paper being provably exactly the same in the court of law.