Excellent point. Also, you have to consider the boards and ownerships stated aims. It was made clear as a matter of policy during OGS' first summer that the club was embarking on a rebuild, aiming to put together a team good enough to contend for titles, with an emphasis on youth. If you're serious about that, that necessarily means a protracted period of investment in signings. Against that background, there's no reason why the transfer funds made available to OGS should be similar to those provided to previous managers in any case. They must be judged against the aims and the approach the Board has itself determined.
If you take their stated policy as they express it seriously, that means accepting that the squad OGS had at his disposal in May 2018 would need wholesale restructuring, and that major investments in top quality players would be required for a period of 2-3 years. There is no other way to turn a defective squad into one that is both young and good enough to challenge for titles. Relative to that, I think it's fair to say OGS has if anything been short-changed so far. Investment was good in his first year (Maguire, Wan-Bissaka, James, Bruno), but hardly extravagant, considering a good deal of the cost was off-set by sales. But I think it's very, very hard to see the backing he got in the last summer window as commensurate with the Board's stated aims. Essentially, what he got was backups for left back and central midfield, and a short-term stopgap striker. It's hard to see that advancing the process very much. And it's obvious that to get where the Board claims they aim to go in the timeframe at hand, there will need to be several additional major investments - in Central defence, at right back, on the right wing, in central defensive midfield and most likely at striker.
It's really not a question of backing Ole, it's a question of backing their own vision convincingly.