The problem is that as a design evolves the price is a moving target.
Exactly, more often than not clients move the goalposts, especially on house extension and refurbisment projects, with items of work added along the way as the design evolves.
As an example, I am doing a project now that started off as a simple reorganisation of a kitchen and a simple extension to that kitchen.
Now...in addition to this, there is a porch to the front of the house, re-wiring throughout the house, new windows to be the existing house, painting and decorating to the enstire house, and, the conversion of a box bedroom to an EnSuite.
Additional works = additional time designing, detailing, specifying, inspecting on site, snagging, etc., etc.
So, on a % basis, the project has a higher value but the fees increase accordingly (to cover the extra time input/work invoved). If the initial fee quote was fixed - fo the work to the kitchen - then with every additional item of work added, you would have to go back, cap in hand, to the client, looking for more fees...that gets annoying (on both sides!).
That's the reason that many architects charge % fees. Where a fixed fee is required - then the client has to be very clear outset that that fixed fee is for a fixed service.
Many architects will also work on a dual fee basis, in terms of starting on a % basis, and, then, when the scope of works has been established (and all the works the client actually wants to do has 'come out in the wash') fix fees from that point on.
As to 'celtic tiger' fees and % fees, bear in mind that a project that is E200K now, would have been likely to have been E300K 6/7 years ago. So, if the architect is still charging a fee of typically 10%...the architect has in effect reduced fees 33% since the 'celtic tiger'.
To answer the OPs query, some architects will exclude what I call 'client supply items', such as timber flooring, tiles, sanitary ware, the kitchen, and the likes, from the build cost/contrcat (and therefore not charge fees in relation to same) if the client is happy to deal with the selection, sourcing and dealing with same.
I believe where % fees get a bad name is from solicitors (conveying houses) and estate agents (selling houses). Hard to justify a % fee for conveying/selling houses based on market value as this varys hugely from area to area but, in theory, the amount of work to convey/sell the house is the same (no matter what the market value is).