Looking at shareware days and games like Jazz Jackrabbit with team of 2-3 devs also. I don't know if Unity would have been necessary. Ofc, after 20 years there is lot more processing power and lot less memory constraints. But still, I am not sure if such engines fundamentally changed anything.

It'd be quite difficult to deploy the processing power and other resources without an engine.

A 90s PC can't do a complex 3d engine because it lacks the grunt. A 2020s game dev can't do a complex 3d engine themselves because they don't know how to do complex 3d.