I'm not an expert in metagames, but from what I've seen, the answer seems to be yes, though there seems to be exceptions as well.
Before the 4th gen., Gengar lacked strong STABs due to having low attack, but it still managed to be in the OU tier. The same was said for Blissey. Still, there were Pokemon that mostly got ignored and was low in the tier list due to lacking strong STABs.
So what's the answer to this?
*awaits the somewhat inevitable mention of Flareon and a strong physical STAB for it, which, admittedly, is one reason I started this topic* --- Praise the Lord, our one true God!
back in the day both poison and ghost were counted as physical moves so nobody would use them on Gengar. However he still had amazing speed and sp.atk and access to strong special moves so he was put in OU.
Well, I'm not an expert, but if you have a decent movepool, would it not be advantageous to have a nice type or two to buff what you've got? I mean, 1.5x can go a looooong way. Also, it's what that stab cover that also helps, right? So, if STAB makes a Pokemon better or lacking in potential, couldn't that facto into what it ranks with, I.e. Tier? --- Official Quilava of White 2 board, a cancer survivor, and a Christian.
You just made me consider a world without the split... and I disapprove! Im frowning... and I feel like I need a hug. But, to answer the question... lets see who, in the top, would be drastically different. Im going to use last month's top 10 for OU and then the top 10 in UU but first, two honorable mentions:
Blaziken: Swords Dance set cant rely on a fire STAB and has to bank on Overheat so it can run mixed. Less threatening for sure.
Garchomp: Most definitly unbanned with the loss of a physical STAB outside of Earthquake. Losing Outrage/Dragon Claw definitly helps his case for coming back, but I dont think he would be less than a solid OU still.
Scizor: No real change here except, possibly, seeing Blaziken back in OU. Im not SURE Blaziken would come back over just losing a physical fire STAB, so Scizor might see no real impact.
Dragonite: His best rainy special attack, Hurricane, is now Physical. THis is pretty dope for his dragon dance set, but losing Outrage/Dragon Claw hurts. It might force him to run Meteor for the extra oomph or just NOT use his Dragon typing except for pure special sets.
Tyranitar: This could be rough. Losing Pursuit sucks and Ttar doesnt have the special attack to still threaten the things he needs to threaten with it. This is really going to hurt his case, but I dont see Ttar ever leaving OU.
Heatran: No real change here I think.
Rotom-W: His offense will stay about the same and his synergy with Scizor isnt effected by this change.
Terrakion: No change here except he might go up. It wont be a huge useage spike so much as a shift.
Ferrothorn: Im honestly not sure here. His biggest weakness is now special only, his fighting weakness is all physical, but I dont see a HUGE change in the layout of his threats because of this. It does ruin focus blasters entirely, letting him focus on the special side.
Politoed: He wont be directly effected by the reversal of the split except for losing Focus Blast. The main impact on Politoed will be the world of sand changing around a bit.
Gliscor: I dont see much here really except one major change. Ice Punch is dead, so all the physical guys afraid of Gliscor have to hope they have the special attack to still kill him with it, or they might as well not bother trying. I see Infernape coming up!
Jirachi: He may have to mix more, but I dont really like Jirachi. It always seems to be flinchax...
So in the top 10 I dont see any sweeping changes. You go much lower and it changes some. Gengar loses Focus Blast AND Shadowball, so he likely falls far. Alakazam gets the elemental punches back, which will be fun. In fact, the elemental punches/fangs are the biggest change I see happening as a result of this. --- Official Togekiss of the BW2 Boards Plothooker - www.plothook.net - Get Hook'd