I will again reiterate the fact that we did not get a story that made much sense in terms of Anakin’s fall.
The Jedi Council had grave concerns about training Anakin, yes? So why make him the student of a just-promoted new “Master”? Stupid! Of course it never matters; we get no hint whatsoever that Obi-wan fails to “train him as well as Yoda”. In fact Obi-wan is supportive of Anakin in ROTS all the time - even when the rest of The Order has its doubts.
As many others in this thread have pointed out, Lucas was unconcerned about making the PT and OT makes sense as a whole. He wanted to tell a specific story about how Anakin went to the darkside even if it was not believable and contradicted his original films!
I think of it like this, Obi-Wan was promoted to a Jedi Knight, who can train Padawan learners, but given permission by Yoda and the Jedi Council because Qui-Gon made Obi-Wan promise to train Anakin. Yoda and the council reluctantly agreed only because Obi-Wan was showing signs of Qui-Gon’s percieved defiance by saying he’d train Anakin without their permission and they didn’t want him to go down the same road. Later when Obi-Wan relies what happened to Luke he tells him “I thought I could train him just as well as Yoda. I was wrong”. The “I was wrong” is key. Obi-Wan believes he could train Anakin as well as Yoda but from the guilt he feels for what happened he feels he failed him as he equally alludes to in his duel with Anakin himself on Mustafar. “I have failed you Anakin. I have failed you.” Yoda was very wise in his wisdom he showed when training the younglings, which Obi-Wan was at one time and when he was instructed partially, and equally when he offered advice to Anakin but he didn’t listen as he was beginning to feel twisted from fear of losing another loved one. I’d say Obi-Wan is supportive of Anakin but in the sense of doing what he thinks is right by him and trying to understand him the best he could. He does the best he can with his limitations and inexperiences of not being ready. This in a way carries over to why they didn’t tell Luke about Anakin right away. They didn’t want to burden him with the responsibility of what happened until they knew he could handle it or at least until it was inevitable as his father told him first. Anakin would’ve been better served with Qui-Gon as his master but unfortunately that wasn’t where fate lead them. Obi-Wan cares and loves Anakin like a brother as he protects him from the prejudices of the Jedi Council as any older sibling would with say a parent or authority figure but wasn’t the master he needed. They’re different responsibilities but connected in their shared circumstance. He did try his best though and ended up being a better mentor to Luke arguably as he taught him to feel but think as he failed to with Anakin. Trial and error.