You aren't going to develop much in the way of usable skills racing against the AI, other than how to avoid moving roadblocks.

For skill development I suggest you join one of the following:
1.
GTP_WRS - Run by GTP members, weekly time trials of various combinations and
online racing too. Everyone gets a license based on their combined time in two TT's and you compete with the best and with those at your skill level.
2.
GTP Online Racing - Find a series you like in a time slot that works for you and race with real people.
3.
Join a Club -
SNAIL is the most popular and you can't argue with 6 GT Academy Finalists!! Lots of others there too that deserve a look.