On these cars, you can make power in two ways: lots of timing or lots of boost.
Boost will make more power. Most off the shelf tunes are like this (catered to street), with only one company that is pretty well known for having crazy timing with minimal boost. It's also a bit "safer" [adding boost instead of timing] generally speaking if not pushing the knock thresholds.
I personally prefer getting more aggressive (but not on the ragged edge) with timing, and dialing back the boost a bit will run cooler in sustained heat (track) situations.
The ECU has tables that compensate for higher IATs and reduce timing as necessary. There is no such table for boost based on temps*. Timing will still get pulled to avoid knock based on IATs, but trying to cram 29psi peak tapered to 21psi on an overspun IS20 turbo near redline will continue generating a TON of heat, and retarding the ignition to avoid knock actually makes temps HOTTER because you're delaying the combustion event, and it'll be more inefficient making more heat in the cylinder. I run 25psi tapered to 17 on my GTI, even with a high flow downpipe. It's "weaker" than most stage 1 tunes. I'll see about 6-7 deg of timing on track near redline when it's 70F outside with IATs within 20-25F of ambient.
Y axis is degrees Celsius for IAT, X axis is RPM. Table is degrees of spark timing removed based off temp and RPM. Stock logic actually ADDs more timing in really low temperatures for reference.
Stock for my .bin for reference:
*In the STOCK ECU logic, there are MANY tables for torque reduction. Two of which include turbocharger speed turbocharger outlet temp - both of which are MODELED without real sensors... so as a result when you tune the car for more power, these things need pushed out of the way. Without doing so, you can't make more power (or at least nowhere near what any stage 1 tune makes). There's not anything inherently wrong with that, but when you're pushing these cars to the ragged edge on track with a street tune, you need to help them in any way possible via lowering IATs. Torque reduction is accomplished in the stock ECU by lowering boost in most cases, and in severe cases by closing the throttle body.
Adding an intercooler *might* make more heat in the cooling system, likely due to more restricted airflow or the more efficient removal of heat from the intake charge air (with that hot air going back directly into the radiator, lowering the delta-T), but most people do an IC + tune at the same time so it's hard to get truly good data.
https://www.datadrivenmqb.com/drivetrain/coolingdata
By and large the GTI has a MUCH easier time dealing with heat than the larger turbo IS38 equipped Golf R.