Your experienced, your opinion, and for sure there are different opinion with gambler who manage to work out with combo/parlay types of betting strategy, I don't have any argument or much better to say that I believe that your personal experience dictates that for you it's better to use a single bet and risk your money compared to a value bet that for me most of the time can ruin your bet.
A single mistake will cause you to lose your pick, but same deal with a single bet if shit happen it will be still the same outcome to you.
You are right in that as you can't win every bet, but the ROI (for me) was more positive than compared to combo bets. I placed a lot of them before and I always got 3/4 or 4/5 and most of the times, the bet with the lowest odd ruined the bet. Same as Klarki, I still place them but these are more funbets with high odds but till date never got really lucky to win them.