Why would that be a problem? If a casino offers favourable bets, what's wrong with using them?
It is a normal habit for a group of bettors to search for the best odds in the market. It can't be considered as an offensive activity or crime. Even a lot of sportsbook promote themselves by saying that they are providing the best odds. Sportsbook usually consider it as offensive when a user place bets on those odds only which have been listed as higher by mistake. Because the bookmaker won't be able to maintain profit in that case.
the user is a professional value bettor. The group use arbitrage tools to target slow feed on sportsbook
This sounds a lot like a company risk to me. Is this a bad thing? The casino is also a professional, if their feed is somehow slower than competitors, they should improve their feed instead. They know very well they'll lose their customers if they offer worse betting terms than competitors. Obviously they don't like players who win, but I'm not convinced we can blame the player for that.
AFAIK, sportsbook doesn't slower the feed for all leagues. The feed is fast for the major sports event. But they make the feed slow for some local and unpopular sports event. In most of the cases, arbitrage bettors or value bettors complaints are related to the local league. They try to take advantages of the slow feed by using arbitrage tools. Everyone will use those kinds of betting techniques if sportsbook consider them as normal thing. Which will effect the sportsbook business in a negative way and they have to shut down their business. Betting sites make the feed slow for unpopular and local league as they don't get the updates on time to time from some local regions. The slow feed helps them to update the odds accordingly with the delayed information.