I've read the two latests posts.
I'll just say that using all spell companions (arcane, essence, channeling and mentalism) I never had any "overpower" problem. Never, like in "I never had any player complain", "I never had to tune anything down" and "everybody has always been happy with my games". I might add "people enjoyed any profession they played".
Speaking about the essence companion, if you factor in the tedium of finding and preparing catalysts, the fact that your players should never, at any rate, be casting spells here and there on a whim (failure + corruption points + nasty things that feed on magic - try using a crafty and double-dealing succubus to manipulate one of your spellcasting PC, it's fun!), the tedium and cost of finding spell lists (teachers or very, very expensive books + guild fees or favors in order to gain admittance) I'd say the book is balanced.
Sure, rituals are powerfull. Costly too. So if the PCs have the means to use rituals whenever they need, you just gave them too much money or power.
Sure, spell lists pack quite a punch or are really usefull. But the book itself goes on for a good deal of pages about guilds and the protection of what they consider their secrets. I don't know for your game, but in mine, PC can't enter the building, pay a fee, spend their DPs and ZAP! know exactly how to cast familiar, staff or elemental magic spells. They have to earn the right to learn these lists, or steal the knowledge.
The professions are actually quite resourcefull. The warrior-mage, in the hands of a player who understands his trade is not full frontal combat but mobility and speed, is actually quite dangerous, as long as he has PPs. The runemage needs preparation, time and planning to use his abilities, so I am okay with the degree of power his high level spells can pack. The mana molder... well played, he can be a nightmare for his foes. I used this profession for vilains. Players always got rid of them using movement spells to get near him and slay him. Before they do this, they were handed their "precious ones" on a silver plate (accompagnés d'une fricassée d'oignons et d'un consommé de poulet, avec sa sauce). Basically, each of these professions trade blatant weaknesses for specialized powerfull spells. Maybe the RMC version won't follow this path, we'll know when we read the book.
Sure, catalysts were giving free PPs. But you don't have to put components or catalysts sellers in every town. Have the PCs look for them. It should be the number one goal of the essence catalyst spellcaster. If you make it too easy for them to use cataslysts, you are giving free PPs to the PCs. YOU, not the rules.
Don't forget the social implications of catalyts! Someone hanging around with jewelry aplenty is bound to be a trouble magnet. Animal body parts should not be sold on every corners of any town or village (well, except for very common ones)... really powerfull catalysts come from fantastic beasts. As such, they should be rare, expensive and maybe sold only on the black market. Plus, the PC should roll for finding the proper catalyst in his many pockets, purses and bags whenever he casts a spell in a tense situation or in a hurry (usually quite the same).
Familiars... well. To put it simply, not only the maluses when the familiar is away ARE a pain for the caster (can't have any of the benefits AND has some maluses... funny when the spellcaster's PP are below 25%) but the death of a familiar is devastating for the caster. Basically, ball spells, gas traps, water hazards or simply a foe that realizes what the animal around the caster really is spell D O O M in fire letters for the familiar owner.
Last, the EssCo was just a toolkit. Don't want something, don't use it. I expect the RMC version to be just the same and I'm fine with it. The book was not perfect, but it is one of the best optional rules book I've read. This approach allowed me to build a complete magic system for RMSS that is unique and well oiled and everybody who've played one of my games enjoyed it.