It's not out of date so much as its woefully understudied. In other words, it could be true, but to my knowledge we really don't have enough data on cotreatment regimens to back it up.

There is a known risk factor of antidepressants in general that is similar to the suicide risk you describe with ADHD medication. SSRI's alone can put you through that process, where motivation increases first, followed after by mood stabilization.

This is why almost all antidepressants mention "increased risk of suicide" as a side effect. If you are starting antidepressants, make sure you actually understand this mechanism and coordinate with your provider and personal support system to ensure you don't trust your half-treated brain to make huge decisions during those critical first weeks.

It's not just suicide - you might find yourself abandoning otherwise positive employment or relationships because you have zero emotional satisfaction but a sudden influx of motivation.

The biggest confounding factor is the chicken or the egg - could the patient's depression be a symptom of their ADHD? That is, could the depression be a long-term psychological consequence of living with untreated executive dysfunction? If their ADHD was treated well, and they felt psychologically "capable" enough to successfully manage their responsibilities and habits, would they still be depressed?

Or is the depression a comorbidity, and it would independently manifest regardless of the severity or treatment of their ADHD symptoms?

It almost certainly varies by and within individuals over time, and can be either comorbidity or symptom, or a combination of both, and there's no real way to tell before treatment.

Some suggest just starting with whichever disorder presents itself more severely in the patient (e.g whichever has more impact on quality of life). Others suggest focusing on depression, as it carries the more immediate risks like you mentioned.

It also unfortunately carries a layer of stigma - like you described, an ADHD patient might be offended that their treatment regimen is designed to "keep them safe from themselves". Which is totally valid clinically, but can be psychologically destabilizing, especially for patients that believe they are not at any such risk right now.

Sorry for replying to your wall of text with a wall of text!

TL;DR: we need much more study on these disorders, especially cotreatment studies, but ultimately you should expect there to be differing opinions and hurdles to overcome on your personal journey.

Everyone should keep an open mind while pursuing treatment, and focus primarily on trying to find doctors and therapists that listen to you and seem to know what they are talking about.