They’re likely just meaning it makes it harder to progressive overload. If you stick to a programme, you know it’s just about modifying weight, reps, rest, time under tension etc. But if you are changing exercises constantly, it can be difficult to know what weight or rep range will get the right results from that exercise since it’s not really comparable to another exercise.

It might be harder to track your progress, but progress will be made nevertheless.

Progress will _only_ be made with sufficient stimulus, and your body will rapidly adapt so the stimulus is not sufficient -- unless you do progressive overload (and ideally occasional deloads too)

You will progressively overload without tracking or thinking about it if you maintain a constant rate of perceived exertion.