Ok, finally.

This MTU 1480 this has been bugging me for years.

Looks like the issue is with Mikrotik's RouterOS.

Keeping everything else the same, same site same btu etc,

Using the TP Link ER605, I am able to get an MTU of 1492.
Proven by the fact that I can ping sites with packet size 1464.
1464+28 (ip and icmp headers)=1492.
Using my RB4011, MTU shows 1480, as expected.
Pinging sites with packet size of max 1452 suceeds.
packet size of 1453 fails.