Reasons to the floating feels probably due to the tyres pressure because it use hard compound UHP the pressure should be 210 not recommend as standard 230, it will much much better grip if you change to soft compound tyre like vios city using

Original tires is Conti UC6 right? Those are not UHP tires.

https://www.tyrereviews.com/Tyre/Continental/

UC6 is under Premium Touring category.

Yep agreed the Almera is more for sedate driving and some overtaking but at 190kmh I think the GB won't be able to sustain those high speeds for a long time as I feel two factors at play here. It uses 0w-20 hence at speeds of 190 kmh the engine oil will wear faster as 0w-20 is more for fuel efficiency hence the oil will prematurely wear faster. Next would be the GB these CVT's are notorious for premature wear hence driving at high speeds will require more frequent GB oil change. That said for a compact car it's certainly the best in its class. Mercedes uses a 4 cylinder 1.3 derivatives for its lower A and C models which speak volumes of this engines potential.

However this 3 cylinder variant is not for kaki racing. It was never meant for racing and never will be suitable but that said for day to day overtaking or get go from traffic lights especially if you live in KL this is a lovely little car.

However with regards to corners is something I feel a little subjective, it is able to take corners precisely but I feel your issue with it taking corners is primarily due to tail winds not this cars outright ability as it is susceptible to wind direction like a smaller car . The cornering though say if you take at speeds of 80kmh is rather neat and not like a shopping trolley like some.B  segments.

Tan Chong I think offers some racing bars and stuff have you considered putting those? Heard it improves the cornering significantly but the ride and weight will be compromised.

0w 20 cannot take prolonged heat at high speeds, you see there is a reason why you see German cars use 0w 40 as at higher speeds the oil will be able to sustain the higher temp unlike 0w 20.  The nissans cylinder wall is 0.2 mm through some diamond and mold coating similar to the GTR hence would only make sense that they use 20. However 20 is not meant for very high temp for prolonged period hence why it would wear faster. Else why do you see the service intervals significantly lower then turbo Germans?