The single point agenda is to “buy low, sell high”. That leads to the question: How do we identify the lows and highs? I think that the low is when the price of the asset/share is less than its value. Similarly, high is when the price is higher than the value. Yes, it is simple.
The key here is arriving at the value of the asset/share. Comparison with other assets (relative valuation using ratios like RoA/RoE), looking at macroeconomic variables, etc. are the thumb rules that people use to arrive at the value of the asset/share. If you like to hold a concentrated portfolio, then you can study the stocks in detail and value them. Valuing the asset directly by quantifying the expected cashflows and cost of capital is superior to relative valuation. I consider valuing the company by projecting the cashflows for the expected high growth period (5 to 10 years) and taking a terminal value after this expected high growth period to be superior to relative valuation. You do not need to bother much about the thumb rules once you have done the hard part of valuing the company. I think that you have already done the hard part of delving into the details and valuing the companies.
There may not be exact comparables of companies to rely on relative valuations. Also, when we are comparing similar looking companies to arrive at decisions, we are intuitively thinking about a pair strategy - buying the company that we think is trading cheap and selling the other that is trading expensive. However, in reality, we do not execute a pair strategy. Consider a scenario where we invested in the company that was trading at cheaper valuations and ignored the company that was expensive but offered the same value. Afterwards, the industry/market went through a bad phase and the share prices declined. We would lose money even if the value of the company that we did not invest in declined more than the company that we invested in. Relative valuation in an industry does not give insights about the valuation levels of the overall industry. However, if we value the company directly, then we are less prone to such problems. In short, I consider relative valuation mostly lazy investing.