How well a team does is not so much dependent on IS or CLAN, as on a number of other factors...
- effective coordination
- leadership (or the team just knowing each other and being on the same page tactics-wise)
- Skill
- Knowledge and experience
- Properly built and leveled mechs
- team moral and aggressiveness
I've seen IS groups roll Clans and visa versa. It almost always comes down to the teams and the points above.
The biggest reason that I see for the IS to usually be on the loosing end of the stick is that there are far more new players in IS mechs. IS mechs are cheaper than Clan, so new players who don't have a lot of Cbills yet tend to buy IS.
Generally clan mechs seem to be owned by more experience players who have been around longer and hence have more cbills to spend.
So ya, the Clan seems to be OP over the IS.....due to the experience difference of the players.
An experienced unit of EMP, SJR, 228, or whoever in Vindicators would probably still roll over an inexperienced, uncoordinated group in any type of Clan mechs.
Even a group of well coordinated newbie PUGs can do well.....
I was in an FW match where I was on an IS PUG team, with a number of totally new players (like guys who shoot the actual gates instead of the gens). And we were up against what looked like at least a 10 man Clan unit on the other side.
Our first wave got annihilated.
Having had enough of that all that day, I decided to try leading.
The tactic was simple enough. The enemy always massed up just over a rise or around a corner from us, and then would roll into us.
I told my guys, to mass up the same way just around the corner or over the ridge and just wait...no poking.
I told them I would run over into the enemy in my Jenner and they were to wait 3 or 4 seconds and then charge in.
Pretty stupid and simple, but it worked every time and we won.
I would charge over and mess with the enemy for a few seconds getting them all focused on me, and my guys would charge into their backs and kill them all. I even survived...but then I am pretty good in a light.
And that was back when Jenners were small, and Oxides were super uber.
That might have worked against one of the uber units too, but only the first time.
I got lucky that time in that the team listened. All too often there are too many rouge players, or too many cooks in the kitchen, or people are just too timid.