Over-betting with the correct range is a valid part of a winning poker strategy. On boards where you have a strong "nut-advantage" (ie. have way more very strong hands in your range than your opponent), it allows you to extract more value with the top of your range, and to bluff more often with the bottom of range.
But against an opponent who over-bets too often with a merged value range (ie. one that consists of medium strong to very strong hands, and few to no bluffs), here's what I would do:
First of all, realize that my opponent is making some potentially difficult situations very easy for me. E.g. when they are incorrectly betting big on a paired rainbow board, I don't have think about letting my unpaired over-cards go. Likewise, I can mostly just fold my second and third pairs, and low equity draws (e.g. backdoor draws, inside straight draws).
Secondly, I would not raise them when they bet. I can count on them to bloat the pot. Also, I don't want them to fold their medium strength hands when I have a very strong hand. This in a way also makes my life easier, because the means I don't have to make risky check-raise bluffs to balance my value check-raises.
Thirdly, I would only continue with high equity draws on the flop, ie. open-ended straight draws and 4-card flush draws. But continue I would with these hands, especially when I'm in position. It's important to be able to have the goods when obvious draws complete. And, if your opponent tends to slow down on the turn when they are in the weaker part of their range, you want to have some draws with which you can semi-bluff your opponent off their equity.
Fourthly, I would not worry about kickers, and be prepared to call down with any top-pair. This will increase your variance, as you will sometimes value cut yourself when they are at the top of their range, but you just have to grit your teeth and do it, because otherwise you risk getting run over. As you do this, you should pay attention to villain's tendencies on later streets, so you can hand read them and make better decisions in the future. Things to look for: Do they slow down with the weaker part of their range? How do they react to scare cards?
Fifthly, when they do check the flop, their turn range is going to be extremely weak! Take advantage by betting every time you see a free turn card.
Finally, I would be hesitant to adjust my preflop ranges too much, unless this opponent is also involved in too many hands. Otherwise, I leave myself vulnerable to being exploited by the rest of the table.
