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.

Yes, of course a single exceptional exception makes it true.

The reason that works for a world class athelete is because they're extremely careful and persistent to periodize and have progressive overload.

Unless the commenter is an equivalent exception, it's bad advice to follow that, or any other, kind of advice from exceptional genetic folks.

It's very difficult to select the correct weight for an exercise when you're constantly changing it up.

What you're describing are simple modifications as a form of progression. Adding a band to a barbell bench press is still a barbell bench press. But going from barbell bench press, to weighted push up, to (incline|decline|flat) dumbbell bench, to iso lateral hammer machine, to smith, to (low, mid high) (cable, bench) flyes, to dips, to ... Is detrimental.

Most folks should try 12 weeks of the exact same exercise per body part with a RIR3, RIR2, RIR1, RIR0 cycle. (increasing weight each week and from cycle to cycle) . And most folks can do a reasonable selection of exercises for a year or two before they need to tweak for imbalance or personal details like insertions, or weaknesses.