Rakan is my second best, most played, and favorite support, and I have to say, he doesn't need his ult touched at all in my opinion. It has a fair amount of damage (100-300 +50%AP), the potential to hard cc the entire team for 1-1.5 seconds, and a good amount of mobility. As Moooose2 said though, just because it gives you movement speed doesn't mean you should rely on just that to hit everyone, you have a w and e for more mobility, flash, and/or protobelt if you want to be really hyped (I wouldn't personally recommend this though), so don't just rely on running into them. Looking at your match history it seems like you stick to the recommended build most of the time, a few things I'd try out to see if you like better would be:
over
, merc isn't bad, but I personally prefer the in combat movespeed over the tenacity.
I know they were changed to synergize more with tanks and enchanters instead of both but
and
still work great with him and a
for the bonus health for
and the item cooldown for both.
is easily the best choice for gold, and
's movespeed active can help start off your engage, or get you out quickly.
The last item is the most flexible on what and when you build it. Obviously
is in a pretty busted state atm, but if your adc is shut down or simply bad it's just going to waste an item slot. If this is the case
to pair with
makes you nearly unkillable in a teamfight,
can work as well depending on the enemy, or
to get out and back in multiple times within a fight.
As you can probably tell, I play Rakan as a high mobility, CC distraction, keeping the enemy focused on stopping me from stopping them, the tank helps make sure I can be a distraction long enough for my team to do their jobs and with
,
, and your e (q too I guess, it's not great but sometimes a little heal is all you need), you can make sure your allies can still do their jobs if your distraction fails. Hope this helps!