Total sectors field in MBR partition entry is 32 bits in length. This means that in case of 512 byte sector size, the maximum partition size is 2^32*512/10^12 TB. Am I correct that in case of 4Kn disks the maximum partition entry size is 2^32*4096/10^12, i.e. 17.59TB? If yes, then this would mitigate the need for GPT?
Yes, if the sector size is actually 4 KiB, the maximum MBR partition size will be 16 TiB. (By the
is in those units I mean the power-of-1024 definition, of which the everyday power-of-1000 definition is an approximation.)
The size of an MBR partition is determined by the address of its first sector and its length in sectors, which are stored in the partition table. See the format at Wikipedia. Originally, sectors were named in Cylinder-Head-Sector (CHS) style, but that limited the disk to 224 sectors (because the CHS address was stored in a three-byte field). Since that was a real shame, Logical Block Addressing - as alluded to in this Microsoft article - was adopted. LBA sector addresses and the sector count are stored in four-byte fields, and (according to the Microsoft Windows 2000 Server Operations Guide) if these fields are present, OSes ignore the CHS fields. Note that the original ATA spec (not the MBR partition table records) only supported 28-bit sector addresses, so that's why you hear about smaller limits on old systems.
After a while, it was realized that a sector size of 512 bytes was a real downer because of this whole 2 TiB limit. For that and ECC/integrity reasons, the Advanced Format appeared (see here for more technical stuff). Drives that physically have 4KiB sectors will present themselves to the OS in one of two modes, 512e or 4Kn, usually depending on their jumper configuration. The
e in 512e stands for emulation - it pretends that its sector size is only 512 bytes, and does some adjustment called read-modify-write when the OS gives it an updated sector. Read more about RMW in this Microsoft article. In 4Kn (
n for native) mode, the drive assumes the OS understands 4KiB sectors and reports the real sector size in the disk geometry. On Windows, you can run
fsutil fsinfo ntfsinfo followed by a drive letter to see the Bytes Per Physical Sector (real sector size) and the Bytes Per Sector (presented sector size). As of Windows 8, Windows supports native 4KiB sectors. You will only be able to use the extra space in 4Kn mode, since the OS knows nothing about the big sectors in 512e mode and therefore can't think about data beyond 2 TiB.
Since 4Kn multiplies the sector size by 8, the maximum partition size (which, again, is defined in terms of sectors) is multiplied by 8 to produce 16 TiB. That applies only to actual partitions; Windows has allowed larger volumes for a long time, which you can create with RAID. I'm sure other OSes have similar functionality. Do be careful, though, as naive disk formatters may refuse to create an MBR partition bigger than 2 TiB if the limitation is hard-coded.
All that said, GPT gives you nice things like being able to have more than four real partitions on one disk and some extra resiliency. You should switch to GPT.