The council will use a process to score the 'value' of every job and then put them in a rank order. It will then apply a pay structure across the rank order and jobs within specified score ranges will be paid the same grade of pay. It appears that this process concluded that the two jobs mentioned were of the same or similar value because they are being paid the same rate. The content of the two posts are unlikely to have been directly compared and this is not necessary to establish their respective values.
If the council does not undertake and maintain this process they are vulnerable to equal pay claims. The 'single status' process referred to in other posts was probably the council (like all other local authorities) seeking to correct its pay anomalies (where work of equal value was receiving different pay) to reduce/remove its equal pay risks through collective bargaining with its recognised unions.
It looks like the drivers and unions previously negotiated and accepted the single status pay outcomes but are now seeking to move their pay up again. I assume the council view is that the value of the work they undertake has not altered so their pay shouldn't change either (or new equal pay liabilities will be created).
Or something like that.
But what you've detailed is EXACTLY the problem. Trying to standardise things that can't be. Go and work for a bank - different roles have different grades and pay scales. In fact almost any private sector company does. Strangely you don't see lawsuits happening then. This whole situation has been brought about by public sector mindsets and the drive to 'make every one equal'. By all means make sure that a female teaching assistant earns the same as a male teaching assistant of the same grade but to make grades equal across wildly differing roles is plain stupid. Unfortunately it would appear to be compulsory to have your common sense gland removed if you wish to become a public sector policy maker ..... or maybe they're just f**king stupid ?