Fair point. I agree. Improving service would attract more passengers.
At the end of the day, incremental upgrades (GO -> GO RER -> Allday electrified -> HSR) will simply make HSR cheaper. Electrified all-day service encourages the elimination of level crossings, which makes the line more HSR-friendly. And you can lay things like concrete ties and higher-speed switches for not much more,
provided they are laid at the time the rail is laid. Building an HSR-compatible incremental RER upgrades might only cost a few percent more.
The problem is staging smartly. Spending in the correct order, with all contractors completing
Many have agreed Metrolinx could do things a little more carefully in staging their upgrades in a more tax-efficient manner to prevent assets from laying idle too long (e.g. less-used track expansions, missing track/switch bottlenecks, and little-used stations that are awaiting GO service expansions to fully utilize).
For me, the whole plan is, on average, quite sensible and needs to continue (e.g. the migration to proper, non-watered-down, all day 2-way 15-min GO service -- with great transit connections like Crosstown LRT and subway included.
Staging smartly in the right order, incrementally, without interim problematic gaps like the current Brampton hourly GO train service -- partially caused by missing pre-requisites. Or the "semi hourly" Stoufville service. Things like the incomplete Georgetown Corrodor upgrades, missing switches, missing tunnels under 401 or other reasons. That's an interim/temporary situation (lasting for a year or few), but should have been avoided in the first place with smarter staging in many ways. While I like the overall GO RER plan, I think that order-of-spending could be greatly improved, so that service deployments are more consistent and quicker.
In some cases, the switch from bus to train service lead to a schedule downgrade, which needs to be compensated-for by more consistent/regular/frequent train service and better municipal transit connections. But there can be a time period where the service gap makes it feel like a far bigger downgrade for a few GO travellers than it should be (e.g. bus service stopping at certain stops, in exchange for trains appearing at an inconvenient-on-foot suburban GO train station) -- until train frequency and municipal bus service catches up, and/or adjustments to connecting GO service are made, etc.