A lot depends on the character template, but I think there are better base pets for spawning than a Cu. To me the lesser hiryu base mana regen is better than the Cu healing. Just my opinion.
Is it absolutely proven that it is infact increased mana regen that is keeping there mana healthy? From my testing certain pet AI's and their default moves are the reason their mana is depleted so quickly and the perfect example is the Cu Sidhe.
I like variety and I hated how UO made the Greater Dragon too good you'd be stupid not to use it and at a glance it looks like you'd be stupid to ignore the lesser or beetles. However I have proven the Nightmare to be a great nox mage pet (training poisoning then back to magery) imo a great 5 slot pet for pvp/pvm, Unicorn is even better but you are forced to be female and don't forget fire steed. Also for pvp 190 dex tsuki looks scary as f*** and a gargoyle with serpentine dragon pfft! The plat/crimson drakes fire/poison edition are super if you have discord+corpse, 100% poison/fire damage can't be ignored + you could buff that with Chiv+talon strike combined with high STR very very nasty and don't forget you can't teach a fire beetle a magic ability so drake > beetle (unless you need a mount). A 125 tactics cold drake has potential too, can be taught chiv etc, you can "correct" a Cu Sidhe/Reptalon but I'll stay silent on that for now.
Animal training is not so black and white (the system needs to be better for sure come on devs) and I'm happy I figured it out but god damn it's so much harder than imbueing, they need to improve quite a few pets though such as stygian drake, Ki-Rin, skree + more necromancy pets, mysticism is boring it's just sleep and more sleep it needs better AI, I haven't even tried spellweaving but i bet it sucks apart from WOD so that needs improving.
Screw lesser and beetles! Get off the wagon!