At this moment i agree Sitthichai is the N1 p4p kickboxing rankings too,considering regularity:
-Holzken had his last big victory sequence over really big names on his division like 3 years ago,in two years his biggest victories was only against Groenhart and Stetcurenko(i am not taking to serious as a strong opposition talking about defeat Daniels Twice).
-Rico Verhoeven almost cleared out his division since being defeated by Semmy on 2012,but considering the last two years,his biggest achievements were defeating a recent top 3 HW twice(Adegbuyi),an top 5 HW at the time of their fight(Zimmerman),A victory over Ghita who was considered the number one HW at the time of their fight(considering semmy was retired,Saki moved to LHW and Verhoeven was said as unproved),but he is not fighting with a lot of regularity like Sitthichai is doing .
-Levin cant be one of the top 3 p4p anymore,he was dominant and probably the second on p4p rankings two years ago,but after that he almost dont fight,only took one KB fight last year winning by controversial decision,and had a recent loss(ok,screwed by referee,but a loss is a loss),his best times was on 2014...
-Saki same Situation of Holzken.
-Kaew have a lot of good wins,but not enough to pass Sitthichai
->Sitthichai last(or first lol) two years on Kickboxing:
Mohammed Khamal(fought with Sitthichai after two year without a fight,but considering all his history it is a really big achievement a victory over him)
Dylan Salvador(a good name,have some good victories and fought with a lot of good guys under FTR)
Murthel Groenhart(pretty inconsistent,but with a lot of good wins and came for that fight with a first round KO victory over a top 10 LW Askerov)
Andy Souwer(Prime passed on their fight,but always a big achievement a victory over him)
Davit Kiria(top 5 lw at the moment of their fight)
Josh Jauncey(good prospect,top 15 at the time of their fight)
-Won a 8 man tournament in one night with two of the 3 fights by KO(even being with lesser names and he was called as an replacement for Kem in a short notice)
- Jonay Risco(Pretty good name,an top 20 for sure)
-Robin Van Roosmalen(highly controversial loss against a top 3)
-Marat Grigorian(big win over a top 5 at the time)
-Superbon(good win over a upcoming promising prospect on the sport )
-Enriko Gogokhia(Top 5 at the time of their fight)
-Davit Kiria again(top 7 or 8 at the time of the fight,but still a big victory)
-Marat Grigorian again(still an fair top 5 on the division)
So on the regularity of the victories Sitthichai is the biggest name on kickboxing right now,bigger than petrosyan considering the recent years,but Petro clearly have a number one spot considering overall.