What we do is define business objectives, set goals, select a strategy, and define the KPIs that will tell us how our tactics are performing against those specific goals.
Some people make the mistake of setting a goal based on a metric you would use for optimization. Your goals should be measurable, but also meaningful to your primary business objective. For example, if your goal is to grow your market share in the fast-growing industry while remaining profitable you would probably use a different set of metrics than someone that has a goal of increasing gross margins while maintaining market share within a mature market. So the first step in your process should be to clearly define your marketing goals.
Once your primary marketing objective is clearly defined, and you have specific goals set, you can devise a strategy and select the primary KPI that accurately measures the progress you are making toward your goal.
If one of your marketing goals includes market share growth then conversion assists will likely be an important factor to consider when evaluating your ad group performance. Once you have your direct response campaigns built out and optimized, the upper portion of your marketing funnel will become critical to driving a larger audience into your funnel, as well as maximizing conversion rates for your direct response campaigns targeting the bottom of your funnel.
I have found having mixed goals in the same campaign more difficult to manage. Ideally, you should create separate campaigns, each focused on the primary marketing objective of that campaign. Move keywords that are primarily targeting the early phase of the buying cycle into a campaign that is specifically designed to contribute to impression assist and click assist conversions. Then optimize those ad groups based on how well they assist conversions.
You will find click assist and impressions assist conversions are easier and more reliable measured if you link Google Analytics to your AdWords account, and also to your Search Console account.