In reference to the patent: US7455257
Is this patent claiming that no scuba diving reel on the market can have a level winding mechanism without infringing the claims of this patent?
In a word: no.
Just picking out words from claim 1, the device must have "a water-tight housing" that is "attachable," "a take-up reel rotatably attached to the housing," "an interior termination attached to" the reel, "a battery-operated motor disposed within said housing and coupled to said take-up reel through a gearing arrangement."
There might be other statements in the patent or the prosecution history (the communication between the applicant and the patent office) that also limit (narrow) the scope of the claims.
Assuming that the claim is valid, it appears that, for example, a purely mechanical (i.e., no battery) device would likely not infringe. Nor would one that did not have a water-tight housing but was designed to operate despite exposure to water.