There is a general trend between bond length and bond strength. Usually, the shorter the bond the stronger the bond. The longer the bond the weaker the bond. Is this always the case? No, it is usually the case. That is why we call it a trend. It is a particularly useful idea for similar bonds. For example a carbon oxygen single bond, C-O, is both longer and weaker than a carbon oxygen double bond, C=O.
Below is a widget in which you can look at the potential energy curves for dihalides (F2, Cl2, Br2, I2). Play with the widget to determine if this trend holds true for all the dihalides or only some of them.