I don't know of any source indicating that Saicho intended to reintroduce the Vinaya (and I have good reason to be skeptical about this myself... not sure why I brought it up actually). And you're correct that Saicho was following a Chinese precedent. But why did he make this move? Think in TienTai terms: he was working expediently (upaya).
Judging from his own writings I would say he thought it best for junior Mahāyāna ordinands to avoid anything that could be called Hīnayāna as per the injunction he quoted from the Lotus Sūtra
. I think he realized this would be politically detrimental and indeed it was what with the criticism he received. He did not even live to see official sanction for his reforms. I think he was acting in a way he felt would be best for his disciples. He probably had such ideas already while studying abroad on the mainland.
Ennin his disciple also went over to China for a few years (even lived through the great oppression of 845 and reported on it with firsthand observations) and recorded encountering monks who also knew Saichō. They spoke well of him. I'm unaware if mainland Tiantai supported such a system of ordination, but as far as I know the government at the time was insistent upon the vinaya, but upon returning home Saichō was free from such restraints.
Namdrol's correct on the contemporary consequences of this move, several centuries after. If you compare today's practice of shaving your head and calling yourself a Punk Roshi or whatever on the basis of inherent enlightenment post-Tendai rhetoric and doctrine (ultimately in all the single-practice schools, not just Soto Zen) to the twelve-year pedagogy Saicho demanded of his disciples... you might struggle to blame Saicho for those contemporary excesses. This would be like blaming Guru Padmasambhava for Aro gTer, which is clearly beyond the intention of the ngakpa tradition.
Tibetan Buddhism despite supporting both vinaya ordinations and various systems of precepts still has negligent and corrupt monastics. Likewise in Theravada. They don't have the same problems as Japanese Buddhism does, but they have their own set of unique problems to deal with. I will say however that the Japanese system is leading to a rapid decline. There is less and less interest in the religious theatre performed by priests for a handsome personal profit, and people have less money to spend anyway, leading to an economic decline, which will ensure closure of temples. When hereditary priests realize there is no more money to be made, or more money to be made elsewhere, a lot of them will just quit. I know some who ordained and go through seminary just because it is a family obligation when in reality they want to work in a company and lead an ordinary life.
Even some Buddhist universities are suffering financial problems. Komazawa (Soto Zen) made a lot of bad investments that went sour in 2008. They had to increase the yearly enrolment to cover that loss. Koyasan University has a shortage of people enrolling, which lead to the bank issuing a statement of concern that they wouldn't be able to meet their financial obligations.
The hereditary system is a catastrophic failure for Buddhism in Japan. It really turned the whole religion into a fossilized tradition of religious theatre and commercial funeral services (such services ain't cheap). Now the demand for such services is in rapid decline the whole thing is crumbling. I don't think Mount Hiei will be converted into condos anytime soon, but in the coming decades Buddhism in Japan will mostly just be the head temples and a few other historical places which serve as tourist attractions and community graveyards.
I think having celibate monks prevents this kind of thing as the temples would be passed down from master to disciple, which in such a case would mean an individual who presumably ordained because they wanted to live such a lifestyle and served their master well enough to merit inheriting the temple. Moreover, such properties would not be private, but held in trust by the greater community, hence little incentive to turn it into a funeral service business.
That being said, though, in Saichō's system the monks are expected to be celibate and unmarried. This is clearly not being followed anymore.
Finally, I'm really not sure why so many English-speaking Buddhists are hung up on the word "monk" as a descriptor for people who hold some kind of vows are not bhikshus or bhikshunis. Insecurity? Attachment? Habit?
I think the problem stems from a few decades ago when you had Zen practitioners calling themselves monks, meanwhile they charge for their retreats, are married, have kids, drink alcohol and own private property...
Obviously the word "monk" is not by default a bhikṣu. The history of the word:
O.E. munuc, from P.Gmc. *muniko- (cf. O.Fris. munek, M.Du. monic, O.H.G. munih, Ger. Mönch), an early borrowing from V.L. *monicus (cf. Fr. moine, Sp. monje, It. monaco), from L.L. monachus "monk," originally "religious hermit," from Late Gk. monakhos "monk," noun use of a classical Gk. adj. meaning "solitary," from monos "alone" (see mono-).
In England, before the Reformation, the term was not applied to the members of the mendicant orders, who were always called friars. From the 16th c. to the 19th c., however, it was usual to speak of the friars as a class of monks. In recent times the distinction between the terms has been carefully observed by well-informed writers. In Fr. and Ger. the equivalent of monk is applied equally to 'monks' and 'friars.' [OED]
Not all bhikṣus live in isolation as hermits obviously.
Also, the word bhikṣu in Buddhism means one who has ordained via the vinaya, but then there are several. Clearly in ancient India there were differing opinions on how a bhikṣu was to behave. The Buddha also gave permission for the vinaya to be reformed if need be.