Ya you are right we dont know. But this game is faster paced than 11. Black mages run outta mp super fast if they dont manage their mp. or if the fight is super dragged out. And we dont know if Smn will be part Blm or part Whm or strictly be summons only. (yes some FF titles Summoners can use Blm only and no whm.)

Ok imagine Ifrit a fight with a summoner. If there is a perpetual cost. Eventually your out of mp cause your not regaining mp like a Blm can in passive mode especially if summons also has white or black magic at their disposal theys either be casting themselvesa bit even making the mp fall faster. Eventually your out of mp and you pet dismisses. Or if they add it what able pet heals are you gonna let you pet die? Cause it will be hit by ifrits fire aura unless its ablilty like second wind that just has a recast. you now have to wait for not only enough mp to resummon that avatar but for it to stay out long enough to be effective. Now you losing on DD for ifrit for the sake of efficiency which is notorious in this game why would you just take a Blm at that point?

Asking for no perpetual cost is not making it over powered. Cause you have to take account that this game right now IS very aoe based and you will have to resummon more than a few times. and if the cost is high you will be outta mp quick. and defintly not overpowered enough to warrent ppl saying. "oh then dd should be able to ws without tp"