Should Casters Prioritize Auto Attacks?

[Allyrion]

You don't lose any damage because you use ruin 2 or bio to move in as a summoner, or procs as a BLM.

For extreme primals, people tend to stack behind titan and ifrit anyway so you'll get your auto attacks there easily. On garuda there's no reason not to simply position yourself right behind her on the non add phases to get your auto attacks.

On caduceus you can stand on his flank at no cost.

ADS repelling cannon and other mechanics will force you to move in and out too much so you'll probably lose dps for trying to melee, plus if you're doing rot then you shouldn't be near melee anyway. If doing enrage then... yeah lol.

Turn 4 can stand behind dreadnaughts np. Anything else not worth running around.

Twintania you get to sit on her for a good part of the early fight so you get your free attacks in. Once twister starts though you have no business being melee.

As a SMN it makes sense. They have good mobility and enough instant attacks to allow for more auto attacks.

A BLM should only do it if they're already in melee because of a fight mechanic. Any movement is a dps loss and you cannot control your procs unless you hold it which is even more of a dps loss.
BLM str is also very low. My SMN is slightly lesser gear has 179 strength compared to my BLM's 88.
Free damage is free and all but if you filled in with scathe when you didn't have to, you probably lost more damage than your auto's would do in that whole fight.

For example, cad might be fairly safe to stand in melee as a BLM but you would have to be very lucky to be one sidestep away from a glowing platform (like you could be at range). Instead, you would have to fill in with scathe.

Plus, this would would only be viable on farm content or ones you stand in melee regardless. For fights where you do stand there, sure - right click the boss and get your damage. Otherwise, don't bother.
For anything you're progressing in, then you probably can't expect complete stability. And that's what's required for a BLM to justify being in melee and gaining dps.