I think limiting stats to 16 max AFTER racial adjustment is the way to go. This will make it more difficult for casters to dominate, while not really affecting martial characters at all.
I also try to discourage dumping stats, but I think that is generally more of a play-style issue, then a balance issue, but the two are linked.
I have found the best way to get the type of characters you want to GM, is to be very straight forward about what you are looking for with the players. I tell my players up front that I don't want them making god wizards, trip/grapple machines, or other types of characters who dominate one type of encounter. I make it clear that EVERYONE is expected to be able to participate in adventuring and social encounters.
Seems mostly reasonable, but here's my issue: I could see myself considering an Oread Armored Hulk Barbarian using the final stats of 14, 10, 18, 10, 12, 8. I wouldn't be a great negotiator, but I could eventually take Intimidating Prowess, and have a reasonable, fairly well-balanced character.
Further, an 18 after adjustments isn't unreasonable when rolling up a character, even rolling 3d6 for each stat (there's a 4.6% chance of rolling a 16 or better for any one of your stats that way, and in a party of four, there's 24 stats rolled.)
As a player, I'd much rather have a lower point buy if I want to play a full caster class than be told I can't play a full caster class at all.
True , but this only works if for some reason you really want to play at a said table.
There is always the third option , which is the players just getting up and finding a table where they doesnt need to hear either houserule given to them.
That said , ofc there are like minded people who probably would like said ruling in their games , in which case a 16 in the casting stat is still something passable.
MY game is based on 15 point buys with an additional point each level gained, including first. No silly '+ 1 to an attribute each four levels'. SADs aren't hurt up there past 17 and the MADs get to fill in easier. Combat casters with 3 or more Ability requirements are becoming common enough to make me read up on them.