Ritwij is defined in Manu 2.143 as follows:
agnadhyeam paka-yajnan agni-stoma-adikan makhan |
yah karoti vrito
yasya sa tasya ritwig iha uchyate ||
2.143. He who, being (duly) chosen (for the purpose), performs the Agnyadheya, the Pakayagnas, (and) the (Srauta) sacrifices, such as the
Agnishtoma (for another man), is called (his) officiating priest.
and Purohit is mentioned alongwith Ritwij in the verse given below:
7.78. Let him appoint a domestic priest (purohita) and choose officiating priests (ritvig); they shall perform his domestic rites
and the (sacrifices) for which three fires are required.
Now, Ritwijs are meant to be respected and thus not degraded. But a Brahmin who officiates for an entire village is considered as degraded.
3.119. Let him honour with the honey-mixture a king, an officiating priest, a Snataka, the teacher, a son-in-law, a father-in-law, and a
maternal uncle, (if they come) again after a full year (has elapsed
since their last visit).
3.120. A king and a Srotriya, who come on the performance of a sacrifice, must be honoured with the honeymixture, but not if no
sacrifice is being performed; that is a settled rule.
3.152. Physicians, temple-priests (devala), sellers of meat, and those who subsist by shop-keeping must be avoided at sacrifices offered to the
gods and to the manes.
Ritwijs who work on behalf of the Sudras are only to be blamed.
11.42. Those who, obtaining wealth from Sudras, (and using that) offer an Agnihotra, are priests officiating for Sudras, (and hence) censured
among those who recite the Veda.
However, according to the the 12th Chapter of Manu Smriti, Purohit, Kshatriyas are all manifestations of the middling stage of Rajas (activity):
12.46. Kings and Kshatriyas, the domestic priests of kings, and those who delight in the warfare of disputations (constitute) the middling
(rank of the) states caused by Activity.
(In 12.46 the word that is translated as priest is Purohit and not Ritwij)
So, there is a fundamental similarity between Purohits and Kshatriyas but I could not prove the same for Kshatriyas and Ritwijs from Manu.