No rate shall be held to be excessive unless such rate is unreasonably high for the insurance provided and a reasonable degree of competition does not exist in the area. No rate shall be held inadequate unless it is unreasonably low for the insurance provided and continued use of it would endanger solvency of the insurer, or unless the use of such rate by the insurer using such rate has, or will, if continued, tend to destroy competition or create a monopoly.