Somehow MC being the least talented person in the series isn't it ? Will he ever become stronger than Suiboku, if not then the title is a total lie.
Talent : MC is shit compare to other japanese person.
Romance : almost non-existence, it feel kinda pitiful compared to the other japanese person in this world too.
Career : Being a guard at a beck and call of some arrogant noble lady, yeah, when compared to other reincarnators he fall short of too.
Time devote to training : 100x times longer than the other reincarnators
Talent, is kind of true. All the other Reincarnators asked for power, and got it. Sansui WORKED for his power; everyone else just got it handed to them (and could be curbstomped by Sansui).
In terms of Romance, Sansui is the only one who is married and has a kid on the way. Sure, his marriage isn't flashy and openly passionate with servile waifus, but is instead based on mutual respect and appreciation. And the archmage kid isn't even married yet, or even gone on a date with his assigned girl, so I don't really see how Sansui's romance is pitiful compared to that.
And as for his career, that's the price of assuring a noble backing, finances, and support in raising his daughter. The other Reincarnators aren't much better.
The Reincarnators in the Arcana Kingdom all serve their backers. Shun (the guy who has Pandora, the Divine Armor) is an enforcer for a Duke, Shouzou (the archmage) is treated as a strategic weapon because he can wipe out entire armies but also has to live in isolation because he can't do anything except rearranging the landscape, and Saiga is set to become the next Duke of Batreble but he's realizing that he needs to see the big picture and how limiting it can be.
And as for the idea of just taking power, look at Ukyo, the Reincarnator who overthrew the Domino Empire and turned it into the Domino Republic, initiating French Revolution-style bloody purges. Not only did he get his entire army wiped out by trying to invade Arcana, but he's constantly overworked trying to run the country because he had everyone who had training to be an administrator executed, his country is still a shithole with its economy in the dumpster, he just barely avoids famine and complete social collapse because his Divine Treasures are basically Star Trek replicators (with unlimited energy, but he only has two so geographic limitations apply), and he still has to come running to the Arcana kingdom every time there's a crisis.