Lee said:
I don't think it's fair to compare the two generations like that. Firstly, the period you speak of didn't have Deoxys-S (or to a less notable extent, Deoxys-D) and obviously didn't have Ferrothorn so Spikes weren't anywhere near as common as they are now and, when they were used, they were normally limited to stall teams but the aforementioned Pokemon make it convenient for offensive teams to have access to Spikes (and abuse them alongside shit like Choice Specs Drizzle Hydro Pump and Choice Specs Latios Draco Meteor to 2HKO 'counters')
Secondly, in my experience it was much easier to fit a Spinner onto your team because defensive Starmie was a decent Pokemon for much of the generation and 'the ultimate set-up bait' Forretress wasn't quite as much the liability he is now due to the lack of shit like Volcarona, Excadrill, Thundurus etc all salivating as soon as they see Forry in Team Preview.
The addition of Deoxys-S and Ferrothorn made Spikes far more frequent however that does not necessarily mean spinning has become much more difficult. Considering Deoxys-E rarely carries any coverage outside Ice Beam and Superpower, Forretress/Starmie can usually switch in everytime to spin the hazards away. This was simply much harder to do during generation 4 when Ghosts were at least twice as common as they are now(just look at the amount of ou teams having a ghost in the RMT archive)
Forretress is just as much set up bait as it always has been, offensive boosters abusing it have become more powerful but the same goes for defensive threats who can stop them proportionally(Evo stone, Explosion nerf, Ferrothorn, Jellicent ,Wish buff, Sturdy buff, Rainstall, Regeneration, Poison heal Gliscor, ..etc).
Offensive spinning(like Starmie used to do) is still possible this generation, Excadrill's running Rapid Spin instead of Sword Dance aren't given enough merit i believe. Its double resist to SR, multiple resists and Toxic/T-wave immunity, which grant the versatility to switch in many times, are often ignored to attempt a one time sweep with SD. Spinblocking Excadrill is very difficult as the Adamant version 2HKO's standard Jellicent after SR damage. Naturally, like offensive teams have always done in the past, you can built your team in such a way that setting up entry hazards is very difficult to achieve due to the pressure brought by repeated powerfull attacks(like PK Gaming's
Enter the Dragon). Or you can limit the total damage done by the hazards by only running those who resist SR and/or are immune to Spikes like in KG's
Solum's Core
I did mention that even if anything else somehow gets past its counters it can still be prevented from sweeping your entire team by something faster. The problem isn't so much that it can crit you or whatever, the problem is that if it does, there's no good way to stop it afterwards unlike with most other things that can be checked with any decent scarfer not just a select group of priority users.
The situation you describe is extremely rare as intelligent battlers won't sacrifice their Excadrill just to do 60%(47% after Poison Heal recovery) damage to Gliscor, considering how easy it is to get it back to full health with 12.5% HP recovery every turn. Not to mention that it is completely ridiculous to say that a pokemon should be banned because it sweeps after landing a critical hit.