If your effort is to get others to consider an alternative to adding onboard reverb, I think that's a reasonable argument to put on the table. If your effort is to say adding reverb to an existing amp is a mistake, I respectfully disagree.
there have been plenty and in my opinion futile attempts to add reverb to an existing amp
I know of many successes in adding reverb to different amp designs. So far, I've personally not had a failure adding reverb to an amp design that I can remember. In ARCHIVES there is considerable information available to help individuals who wish to attempt this. There have certainly been quite a few success stories posted on the forum in this endeavor.
and putting the reverb in front of the amp not only gives you reverb, it also saves your amp.
I don't know what this means? How does putting reverb in the front of an amp
save the amp? There are plenty of 50 yr old amps with reverb integrated within the amp. If you're simply implying it means you can keep the amp from experiencing any changes ......... then OK. Saving an amp sounds like your trying to protect it from harm.
I put quite a mile of footwork to arrive on that conclusion and for some reason you may not agree to, reverb sounds best if applied first in the signal chain.
Sure, this can definitely be a preference thing. If you like reverb in front of an amp that's great.

I've run my Digitech RV-7 reverb pedal in front of an amp and enjoyed the tone when playing "clean". I thought it sounded quite nice. However, I prefer it further down the signal chain especially when using overdrive. Simply my preference. The only time I don't have my reverb pedal in an effects loop is when I play a friend's Fender Champ.
There are individuals who prefer time signature effects (reverb, delay, chorus, flanger, etc ) to be later in the signal chain. That's why you see amps with passive and active effects loops further down the signal chain.
I personally prefer overdrive to be reverbed than reverb to be overdriven. That doesn't mean the tone I prefer is "better". I'm not inferring that. There are simply different personal preferences for tone. I certainly would not "caution" someone from using a reverb pedal upfront. It's a fine way of adding reverb. And you can simply move that pedal from one amp to another one. Good argument for considering a reverb pedal.
With respect, Tubenit