Look at the tonnage of the type 26 on wiki (6900);
Type 26 frigate - Wikipedia
Look at CSC (8080)
Canadian Surface Combatant - Wikipedia
Now look at the AUS hunter class, which also took the AEGIS, slapped it on the T26 at 10k tonnes, so outweighing an Arleigh Burke
Hunter-class frigate - Wikipedia
Sure, ISI was involved, but it was all Canada's decisions. Cumulatively making CSC bigger than the base design, so fair bit bigger on what the combat package bid was for. JSS is the same size as what is in the NSS package.
Don't get me wrong, I'm not an ISI fanboy, but we wanted a complicated, manpower intensive combat system, with a huge radar up high, so the only way that works is with a bigger hull.
Bigger hull means bigger assembly bays, bigger mega block assembly area, bigger launch requirements etc etc.
If you want an actual MOTS design for a ship, don't change anything (except domestic power to 110/60 Hz vice 220 50 hz, which is easy). If you want project cost increases, Canadianize the base design, select totally different combat systems, and select different parts for every widget onboard.
A lot of the Canadianization requirements are driven by GoC rules for Canadian content. A lot of delays (which lead to cost increases) is related to GoC oversight and accountability requirements that are also built into the contract.
Don't get me wrong, ISI won't lose money on any of this, but if we had stuck within the design envelope we specified, and didn't make major equipment selection items impacting that, ISI wouldn't be doing a major shipyard upgrade to build it.
CSC will give major capabilities (if we don't screw it up and cheap out on maintenance or training), and may allow us to credibly assist in BMD defence, which seems like a good thing, but none of this is cheap. The world is also a different place now compared to what it was 14ish years ago when the NSS tender was drafted, so does it make sense to consider significantly increase capabilites of CSC while we can? Once it's built it's pretty much fixed for the next 30 years.