If you are using pressure Ho-oh to use defog on it, you might as well not use Ho-oh, regen is absolutely too good to pass up on. In Lugia's case, well I would consider defog on that (maybe) since Lugia is often hazard bait, and pressure might help in some scenarios. However, running reflect and defog on the same set doesn't look appealing at all, you either miss out on recover, phazing or status- all three needed for Lugia to perform.
Arceus has been really solid as a defog user so far. Arceus-Rock with Defog/Recover/Judgment/Will o Wisp can handle SD Arceus, burn random things, check Yvetlal and counter Ho-oh and of course clear hazards while Arceus-Psychic can use a similar set to combat Mewtwo formes instead of Ygod and Ho-oh. Skarmory is solid too, very hazard resilient, reliable recovery, spreads status/taunts etc. The main problem is that you often wished Skarmory could run taunt and toxic on the same set with defog, but sadly you need phazing and recover. Haven't personally tried any Giratina forme but I can see both working quite well, even though wasting two moveslots for RestTalk recover is a bit much. Giratina-O still has nice offensive presence, priority and the buffed will o wisp and you can use wish support or something to keep its health up- or just play offensively enough so that your opponent pretty much only gets one chance to get hazards up, since Giratina-O without recover will probably be able to defog at least once. Scizor is solid, it checks Xerneas pretty well too and doubles up as an additional E-killer check with toxic or superpower.
Defensive defog Zapdos can't check anything big in the metagame and Empoleon gets wrecked by Thunder Palkia and LO Aura Sphere Dialga (which is quite common on offensive SR Dialga) and it doesn't get recovery besides rest. The thing about "previous Rapid Spinners would never be considered in Ubers without Rapid Spin" is that most spinners actually did more things that just spinning. Defog users like Zapdos can't exactly provide any other team support that defog while gen5 Forretress for example, lures in Ghostceus and Giratina-O with Toxic, Spikes up on Fat-Tina, checks SD Arceus, forces out Ferrothorn etc.
To sum it up, defog is perfectly viable- for stall you get the opportunity to blow away offensive team's hazards, which is detrimental as stall teams can't take hits with multiple layers up. For sun offense, the usage of Ho-oh is suddenly easier, and Ho-oh is amazing so defog is very viable on those types of teams as well. The main catch is that defog Arceus is quite costly opportunity-wise. You can't run CM (unless maybe Steelceus) if you want defog support from your Arceus-Forme, and for Ho-oh weak Arceus Formes like Figthing and Fairy you will be hard pressed to find a moveslot for both toxic and stone edge together with defog (both toxic and stone edge are staples and very important on donkeyfightceus for example). Defog Skarmory contends with the fact that it can't use Taunt+Toxic+Recover+Phazing+Defog all at once so that will have to be taken under consideration too.