Modern Age? Definitely not. I think even by the end of the manga after Tanjiro receives every single power up in the KnY universe the strongest is Himejima Gyōmei.
This man has been repeatedly stressed and validated to be the single strongest Demon Slayer in the series and I dont think that changed even upto the end of the manga. Despite Peak Tanjiro and a few others like Sanemi coming close in my opinion Himejima still is the strongest and has the best showings in the verse.
Just in his first actual fight in the series Kokushibo, the strongest Upper Moon and the second strongest demon in the entire series straight up admitted he was the strongest human he had seen in 300 years, with a peerless body crafted to the absolute peak of human perfection. This is before Himejima activated his mark or unlocked See Through World or Red Blades which increases his power exponentially.
In the strength rankings for the Hashira Himejima ranked top spot by a significant margin to the point that his strength was considered “overwhelming”. Unmarked Himejima is physically the strongest base human in the series.
On top of this Himejima without a mark was able to go toe to toe with a “base" Kokushibo for a significant while and performed better than both a marked Muichiro and Sanemi. This feat alone puts Himejima above most of the Uppermoon considering a marked Muichiro was able to blitz an uppermoon (5) but was unable to do anything to Kokushibo.
Himejima later unlocks See Through World and Demon Mark which increases his strength, agility and perception to ungodly levels to the point that he could outmatch Kokushibo at cqc and tear an ear off and could likely have soloed him if Kokushibo didn't power up to his final form.
Heck his weapons were powerful to blow a hole through Kokushibo. What's funny is that if Kokushibo didn't have the insane regeneration of demons he would have died at the spot after a single attack. On the other hand Himejima was able to tank a bunch of his blows without too much trouble.
This is before he unlocked the ability to turn his weapons into Red, which in the demon slayer universe imbues weapons with the power to slow down regeneration, and deal increased and lethal damage.
A fully buffed peak Himejima should be able to solo all uppermoons aside from Kokushibo (UM1) with mid to high difficulty. This is further backed up because Kokushibo early in the series could blitz Akaza who was the 3rd strongest Uppermoon and yet Himejima was stronger than “base" Kokushibo.
He easily has the highest Attack Power of all demon slayers and possibly the fastest speed as well, second only to maybe Shinobu or peak Zenitsu (Thunderclap+Flash+Godspeed mode). His weapons have the highest range of all Hashira.
On top of that his special Juzo Beads projectIles he can throw to slow down the movements of demons.
Overall I believe his immense stats and well rounded arsenal make him the strongest human character in the series aside from Yoriichi of course, and he was the strongest modern demon slayer throughout the run of the manga.