TheOceanAgency
I think EGOL says a lot with his comment re types of sites. An ecommerce site will typically take more time and attention than a 15 page attorney site. Sites that are large, publish a lot, have a reference type role, etc. are others that require more time and attention Do you have a role in development or are these all fully completed sites? Do you have a developer who assists you with changes, etc.? Can you take specific SEO needs to a developer who can execute the more complex items?
We are an agency and our staff is not set up as handling X # of clients but having varying roles. Within those roles, we are all constantly learning the roles of others. An example is copywriters learn SEO, HTML, etc. Our head of Local is quite competent at handling full site 301's and she is not a developer - she was taught by our head of dev.
For you, if you do not have a process and are instead running "helter skelter" it will be more difficult. So, let's break it down based on what you have here (and I am sure you have other "roles" you take on from time to time as needed.)
Onsite Optimization: Assuming you did not take on 9 new clients with bad on page, you should get to a place where the on page, on site is fairly stable. (Your data gathering/reporting should show when there is a problem). If you are having to redo onsite regularly, there is a problem that needs to be handled - what is causing it to be unstable? (CMS issues for example).
With link building, what are you doing there and what are you outsourcing? This is very labor intensive role and may not be a highest and best use of your time as an SEO professional. (Remember, whomever is doing it, you must inspect what you expect.) You state that **"...with some outsourcing when it comes to content creation (things like infographics, articles and some linkbuilding efforts)." **For us, we create a lot of content and that is why we have a copywriting team and a director of media who oversees that role. Beware if you are getting too involved with how the outsourced pieces are done - have a result you want and do most of your input at the beginning and not on correcting at the end.
Last, you handle monthly reporting. This, too, is one of those that when handled correctly in the beginning, should have little impact on your time. If you are spending a lot of time on it, then I would guess you do not have it set up in a cogent and manageable way. Usually, each client is getting something different as opposed to a more standardized reporting with specific 'unique reporting' that is set up early in the relationship.
If, your role is also taking all the data, deciding what is wrong/right, then creating a plan of attack, then meeting with the clients, etc. You are likely overburdened and have a role that needs to be organized. NOTE: I am NOT saying you are disorganized; I am saying the role may be. There are lots of ways this happens, but typically in an agency that is less mature, you take on clients at a lower cost to them. In order for the agency to profit some will just provide less resources; worse than that is when they just do not deliver on their promises.
So, I am guessing there is no "answer" in what I have given you. Hopefully, I have given you some things to think on and a way that you might be able to be of greater benefit to the agency - creating an organized role to minimize waste of resources.
All the best,
Robert
PS As to ration of in-house to outsourced efforts: I only outsource one thing and that is SEO Audit backup. When I do an audit, I go outside to one of three or four Moz top rated SEO pros and have them do back up audit for me. Not a full audit, but an overview of mine for errors or omissions. (And, rarely, for a second audit if there is apt to be a question in a legal or more complicated sense.)