You mention changing level up bonuses to apply to +1 to two stats. Saga Edition did this and it worked to make all characters significantly broader without losing ability. One physical and one mental helps tier 1s a little (wizard gets a bit more AC and to-hit with rays, battle cleric is even more viable) and helps martials a lot.
May be worth noting the OGL never explicitly calls out how ability scores increase with level. Though since Pathfinder use the same rate and the SRD still mentions
Treat monster Hit Dice the same as character level for determining ability score increases. This only applies to Hit Dice increases, monsters do not gain ability score increases for levels they "already reached" with their racial Hit Dice, since these adjustments are included in their basic ability scores.
I assume that since it can be reverse engineered from the example advanced monsters that are
covered under OGL there's no legal issues. I think this is the case for a few other rules regarding advancement as well (feat rate can clearly obtained with the same process).